Design and development of a miniature self-propelled ultrasonic piezoelectric plate motor

This study developed a miniature self-propelled ultrasonic piezoelectric plate motor designed for precise actuation in a compact structure. This motor was comprised of a 9 mm × 6 mm × 0.3 mm stainless steel plate and a 0.2 mm thick PZT actuator with free edges to avoid complex fixtures. To enable self-propelled motion, the superposition of Φ₂₀ and Φ₂₁ modes was used to generate the traveling waves based on the Two-Integer-Frequency, Two-Mode (TIF-TW) driving method, which drove the motor in the same direction. Since no analytical solution exists for a plate with free boundary conditions, the Rayleigh quotient method was used to approximate mode shapes and resonant frequencies, and finite element analysis (FEA) was performed for validation. A cost function based on the Hilbert Transform was introduced to optimize wave stability and reduce standing wave effects. FEA results confirmed that superimposing Φ₂₀ (26 kHz) and Φ₂₁ (52 kHz) can generate stable traveling waves. With time-dependent simulations, we obtained a consistent wave amplitude range of -3.02 × 10^-4 mm to 2.9 × 10^-4 mm, ensuring predictable micro-displacements. Our findings demonstrate the feasibility of our proposed ultrasonic piezoelectric plate motor for compact ultrasonic actuation and self-propelled motion.