A miniature longitudinal-bending hybrid linear ultrasonic motor inspired by the planar hinged five bar mechanism.

Inspired by the double crank planar hinged five bar mechanism, a longitudinal-bending hybrid linear ultrasonic motor with compact miniature is proposed and tested. In order to realize miniaturization, it adopts a bonded-type structure. Four lead zirconate titanate (PZT) piezoelectric ceramics are distributed equally into two groups and bonded to the two ends of the metal frame, and then, two voltages with a phase difference of 90° are applied to each of the two groups of PZT ceramics. Subsequently, the first-order longitudinal vibration and second-order bending vibration generated by the motor combine with each other at the tip of the driving foot to form an elliptical motion trajectory. According to the theoretical kinematic analysis of the free beam, the initial structural dimensions of the motor were designed. Then, the initial dimensions of the motor were optimized, and the zero-order optimization algorithm was used to achieve the purpose of longitudinal and bending resonance of the motor, and finally, the optimal dimensions of the motor were obtained. A prototype of the designed motor was made, followed by experimental tests on the performance of the prototype, including mechanical output. The maximum motor speed without load at 69.4 kHz is 134.57 mm s-1. Under 200 Vpp voltage and 6 N preload, the output thrust of the motor is about 0.4 N at the maximum. The actual mass of the motor is about 1.6 g; therefore, the thrust-to-weight ratio was calculated as 25.

A novel thin single-phase drive linear ultrasonic motor.

A novel thin single-phase drive linear ultrasonic motor is proposed and tested in this paper. The proposed motor exhibits bidirectional driving via switching between the right-driving vibration mode (RD mode) and the left-driving vibration mode (LD mode). The structure and working principle of the motor are analyzed. Next, the finite element model of the motor is established and the dynamic performance is analyzed. A prototype motor is then fabricated, and its vibration characteristics are established via impedance testing. Finally, an experimental platform is built and the mechanical characteristics of the motor are experimentally investigated. The maximum no-load speed of the motor is ∼159.7 mm/s. With 8 N preload and 200 V voltage, the maximum thrust force of the motor in the RD and LD modes are ∼2.5 and 2.1 N, respectively. The motor possesses the advantages of being light in weight and thin structure and exhibiting an excellent performance. This work presents a new concept for the construction of ultrasonic actuators with bidirectional driving capacity.

A novel hybrid mode linear ultrasonic motor with double driving feet.

A novel standing wave linear ultrasonic motor with double driving feet based on longitudinal-bending coupling mode is designed in this study. The motor adopts the bonded-type structure, and four pieces of piezoelectric ceramics on a metal beam are divided into two groups. Two voltages with 90° phase difference are applied to two groups of Pb-based lanthanumdoped zirconate titanates ceramics, respectively. Then the first longitudinal and second bending modes generated are superimposed on the stator, which can produce elliptical motion trajectories on the driving feet. The excitation method and driving mechanism of the motor are illustrated in detail. A finite model of the stator is established in the ANSYS parametric design language interface, and the operating mode of the stator and motion trajectories on the driving feet are discussed. The prototype is fabricated, and its impedance characteristics and mechanical output performance are tested. The results show that the maximal no-load velocity of the motor is ∼147.78 mm/s under a voltage of 200 V and a preload of 3 N. The maximum thrust force is ∼1.1 N when the voltage and preload are 200 V and 6 N, respectively.

Optimization analysis of piezoelectric actuator based on energy transfer.

Based on energy transfer theory, the power flow method is used to optimize the piezoelectric actuator to improve its output performance. First, the mode analysis of the piezoelectric actuator is performed, and the actuator is discretized according to the mode nodes of the operational mode. On the basis of the Norton's equivalent circuit, the equivalent mechanical network of the actuator is established, and the expression of power flow is imported to the mass block of driving foot. Second, on the basis of the actuator power flow expression, simulation analysis is conducted to obtain the influence of actuator parameters on the power flow amplitude for optimizing the driver parameters. Finally, a test platform is built to compare the improved piezoelectric actuator with the original one. Results show that the output force and power of the improved piezoelectric actuator have increased by 8.3% and 22%, respectively, to verify the effectiveness of the optimization method.

A novel high thrust-weight ratio linear ultrasonic motor driven by single-phase signal.

This paper presents an ultrasonic motor with a high thrust-weight ratio. The miniaturized motor is 13 mm × 5 mm × 3.8 mm in size and uses the first-order bending vibration mode (B1 mode) and second-order bending vibration mode (B2 mode) to realize bidirectional movement through a single-phase driving signal. The theoretical trajectory and output thrust of the motor driving foot are initially studied. Subsequently, a finite-element model of the motor is established, and its dynamic performance is studied. Next, the prototype of the motor is fabricated and tested. The results show that errors in the B1 and B2 modes are 1.976% and 0.436%, respectively. Finally, an experimental setup is constructed to test the mechanical properties of the motor. The maximum output velocities of the motor is approximately 158 mm/s at 58.917 kHz in the B1 mode and approximately 137 mm/s at 113.581 kHz in the B2 mode. The maximum thrust force values of the motor in the B1 and B2 modes are approximately 1.32 N and 1.08 N, respectively, with 7 N preload and 120 Vpp voltage. The overall mass of the motor stator is 1.0 g, so the motor thrust-weight ratio reaches 134.69.

An Equivalent Circuit of Longitudinal Vibration for a Piezoelectric Structure with Losses.

Equivalent circuits of piezoelectric structures such as bimorphs and unimorphs conventionally focus on the bending vibration modes. However, the longitudinal vibration modes are rarely considered even though they also play a remarkable role in piezoelectric devices. Losses, especially elastic loss in the metal substrate, are also generally neglected, which leads to discrepancies compared with experiments. In this paper, a novel equivalent circuit with four kinds of losses is proposed for a beamlike piezoelectric structure under the longitudinal vibration mode. This structure consists of a slender beam as the metal substrate, and a piezoelectric patch which covers a partial length of the beam. In this approach, first, complex numbers are used to deal with four kinds of losses-elastic loss in the metal substrate, and piezoelectric, dielectric, and elastic losses in the piezoelectric patch. Next in this approach, based on Mason's model, a new equivalent circuit is developed. Using MATLAB, impedance curves of this structure are simulated by the equivalent circuit method. Experiments are conducted and good agreements are revealed between experiments and equivalent circuit results. It is indicated that the introduction of four losses in an equivalent circuit can increase the result accuracy considerably.