Piezoelectric Motors with a Stepping and a Resonant Operation Mode

Ultrasonic linear piezomotors have several advantages compared to electromagnetic motors in specific applications such as in high-vacuum conditions and where no magnetic field is allowed. These compact directdrive motors are fast, but low speeds and high-resolution positioning are difficult to obtain. On the other hand, several non-resonant piezosteppers were developed, resulting in very accurate linear motors, but with a low speed. This paper presents two prototypes of piezoelectric motors that can work in a stepping mode as well as in a resonant mode. The stepping mode allows a very accurate, but slow actuation. The resonant vibration mode allows coarse, but fast positioning. The first prototype is a linear motor, using one eigenmode of the structure in the resonant vibration mode to achieve high speeds. The second prototype is a planar motor, using three eigenmodes of the structure at resonance. Both motors combine the fast positioning capability of resonant motors with a stepping function enabling fine positioning in the nanometer range.