3. Vibration System Design and Implementation

According to operating frequency, vibration devices can be divided into two groups: resonant mode systems and nonresonant mode systems. For a resonant system, a sonotrode (also called a horn or a concentrator) vibrates at its natural frequency, transferring, and amplifying a given vibration from a vibration source, which is usually a magnetostrictive or piezoelectric transducer. It can achieve higher operating frequency and greater energy efficiency compared with nonresonant systems. However, its vibration trajectory cannot be controlled precisely owing to the nature of resonant vibrations and the phase lag between excitation and the mechanical response. A nonresonant vibration device applies forced vibration theory and can produce variable vibration frequencies, which are always less than its natural frequency. Compared with resonant systems, nonresonant systems tend to achieve higher vibration accuracy, and it is easier to achieve closed loop control of the vibration trajectories under low-frequency conditions. As one of the most promising ultraprecision motion mechanisms, a flexible mechanism driven by a piezoelectric actuator is widely applied in ultraprecision manufacturing for the optical, biomedical, and aerospace industries because of its merits such as rapid response, high movement resolution, no friction and wear, and compact structure, and also, no lubrication is required. Nonresonant vibration-assisted machining with the working frequency less than the device’s natural frequency makes precise closed loop control possible and has received increasing attention. However, the full decoupling mechanism increases its design complexity and leads to some sacrifices in performance. In addition, the piezoelectric actuator can only withstand compressive stress, whereas the coupling motion mechanism generates shear stress and can cause damage.