A new inchworm piezoelectric rotary motor with optimized vibration and frictional slipping effects

Inchworm rotary motion with high-precision and large-stroke properties is increasingly required in micro/nano alignment applications. However, the precision of current piezoelectric inchworm motors is severely deteriorated by poor step consistency under different frequencies because of undesired contact vibration and frictional slipping. In this article, an inchworm piezoelectric rotary motor with high step consistency is developed. A new compliant soft contact and rotary mechanism (CSCRM) is designed and optimized to achieve soft and stable contact, and then rotate the output platform in sequence, passively suppressing vibration with two-level compliant contact stiffness. Importantly, to analyze the triggering condition of frictional slipping, a contact-friction model is presented to build the relationship between the driving signals (including acceleration) and the friction. Then, the boundary conditions of frictional slipping are deduced from the contact-friction model and used to optimize driving signals in value, sequence and shape. FEA simulation verifies the optimized results of mechanical parameters. In addition, a prototype is fabricated and tested with comparative experiments. The experimental results uniformly confirm that the developed piezoelectric rotary motor can achieve microradian resolution with 3.3 $\mu$rad, speed of 42.81 mrad/s, and load-bearing capacity of 2 kg in a highly linear and stable manner. More importantly, the contact vibration and frictional slipping are nearly eliminated, leading to almost no rollback and highest step consistency among current literature, i.e., 93% within 100 Hz. It is also worth noting that the designed motor can continuously work across different frequencies without readjusting the initial gap.