Nonlinearity and resonance frequency shift make it difficult to control the operation of the traveling-wave ultrasonic motors (TWUSMs) in a wide velocity and load range. In this paper, a velocity control scheme based on the stator vibration amplitude and the parallel resonance frequency (VCBVF) of TWUSMs is proposed. Then, the stator vibration amplitude (SVA) and parallel resonance frequency (fp) are detected by a transformer ratio-arm bridge. Based on the linear relationship between the velocity and the SVA of TWUSMs, the proposed scheme achieves the control of the mechanical loop and the electrical loop. The linear relationship between the velocity and the SVA makes the mechanical loop achieve the target velocity efficiently, according to the SVA, and the electrical loop could provide the target SVA quickly. Experimental results show that the response time of velocity is 3–4 ms under different load torques and the overshoot is less than 22%. In addition, the proposed scheme improves the efficiency of TWUSMs due to fp tracking. Due to directing the SVA control, the proposed scheme can heighten the velocity response and the load adaptability of TWUSMs, and promote the application of TWUSMs under various conditions.
Traveling wave rotary ultrasonic motor with double vibrators can improve the output performance effectively. However, the rotor has to be energized through a slip ring, which increases the complexity and reduces the reliability. Inheriting the concept of two traveling waves propagating in the stator and rotor, a dual traveling wave rotary ultrasonic motor energized only in the stator is proposed. By analyzing the oscillatory differential equation and the contact particles motion, a traveling wave is found in the rotor and the drive mechanism of dual traveling wave is studied. With the resonant rotor adopted, the consistent eigenfrequencies are calculated by finite element method and verified by an impedance analyzer. The performance experiment presents that the dual traveling wave rotary ultrasonic motor is superior to the motor with single traveling wave. The no-load speed is 60 rpm and the stalling torque is 0.85 Nm. Additionally, compared with a reported motor with double vibrators, the proposed motor presents the better output performance and the simpler design.
To improve suitability in applications with high dynamic performance requirements, the transient response characteristics of high-power piezoelectric transducers should be studied quantitatively. This paper proposes the vector reduction method to solve the complex transient equations and obtains a transient matching scheme clarifying the mechanism of electrical matching resistance on electromechanical damping. A matching scheme with a combination of full-bridge inverter, transformer and series LC circuit is designed and validated, which can provide suitable electrical damping without causing energy losses. Consequently, the experiment verifies the transient properties of the proposed scheme. For a typical piezoelectric cutting transducer with 100.8 ms response time, our scheme is verified to have high dynamic performance within frequency response time of 5.5 ms and vibration response time of 15.0 ms.
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