The Performance Analysis and Optimal Design of Traveling Wave Ultrasonic Motors

1 Principle Demonstration Simulation Software Main Function Module The main function of this section is to visually demonstrate the working principle of the ultrasonic motor in an animated way. There are mainly demonstrations of travelling wave in the stator, demonstration of the elliptical trajectory of the surface of the stator tooth, and demonstration of the driving and power output mechanism of the ultrasonic motor, so as to have an intuitive understanding of the working principle of the ultrasonic motor. In addition, simulations can also be performed to demonstrate the distortion of traveling wave and elliptical motion generated in various non-ideal situations (such as unequal amplitude of two phases, or phase difference not equal to 9tb, etc.).

2 parameter setting capital project: National Natural Science Foundation of China (50235010) The main function of this part is to input all kinds of parameters of ultrasonic motor A-wave ultrasonic motor performance analysis and optimization design values ​​(mainly stator, friction layer and pressure Electrical ceramic material property parameters, geometric size parameters, and other parameters such as pre-pressure, modal order, etc., are used for subsequent performance prediction or simulation parameter analysis of the ultrasonic motor.

2.3 Performance prediction This part can calculate the transient response of the ultrasonic motor under a given amplitude of the input alternating voltage excitation (such as start-off characteristics, overshoot and stability, according to the parameters of the given ultrasonic motor parameters. Amplitude, etc.) can also calculate the motor speed corresponding to different load moments at a given preload, ie the load characteristic curve of the ultrasonic motor. The main function of this module is to predict the output characteristics of the ultrasonic motor at the design stage in order to check whether the design prototype can achieve the expected performance.

2.4 Parameter Analysis In order to evaluate the dynamic characteristics of the ultrasonic motor, we have proposed the following indexes: the natural frequency of the bending vibration of each order of the stator; the modal mass and the modal stiffness corresponding to each bending mode; the stator based on the piezoelectric ceramic excitation. The response displacement, vertical vibration velocity amplitude and the corresponding tangential speed of the rotor.

Based on piezoelectric ceramic excitation coefficient and electromechanical coupling coefficient; piezoelectric ceramic / elastomer composite stator vibration equivalent circuit equivalent capacitance and equivalent inductance.

Piezoelectric ceramics correspond to clamping capacitances of various bending modes.

These dynamic characteristics description indicators include both mechanical and corresponding electrical characteristics, and more concentratedly reflect the dynamic characteristics of the ultrasonic motor. In particular, the electrical characteristics index has only been obtained after the ultrasonic motor is manufactured and measured using the equivalent circuit principle. This article can directly calculate and provide the predictability of the ultrasonic motor and can pass it effectively. In order to use this software, examples of simulation results of modulo-order analysis of stator dynamic characteristics are presented.

3 principles of optimization design of 3-wave ultrasonic motor The design of ultrasonic motor involves the determination of many parameters, each parameter has more or less influence on the dynamic parameters of the ultrasonic motor. When we design and parameter the ultrasonic motor Based on the following principles: Ultrasonic Motor Performance Prediction and Parameter Analysis Procedures The parameter analysis diagram of the dynamic characteristics of the stator has additional conditions, such as the maximum speed, locked-rotor torque, and the sensitivity of external load changes (load characteristics (Soft and hard) and so on, and even restrictions on size (outside diameter, thickness), weight, etc. In some special occasions such as aerospace, precision instruments, micro-electromechanical systems, etc., sometimes these will become strictly obligatory Limited conditions. Therefore, at the beginning of the design of ultrasonic motors, the most important design requirements should be clearly defined.

This paper believes that the no-load speed and locked-rotor torque of ultrasonic motor are two important design indicators. According to the characteristics of the load characteristic curve of ultrasonic motor, after determining these two indexes, the load characteristics of ultrasonic motor are roughly determined. Another design indicator is the diameter of the stator. The stator diameter has a certain relationship with the no-load rotation speed and the locked-rotor torque. After the no-load rotation speed and the locked-rotation torque are determined, the diameter of the stator also has a general range.

In order to standardize the product design, a relatively regular value is generally selected in advance.

The parameters that directly determine the design parameters closely related to the design index and the no-load rotation speed mainly include the working modes (wavenumber, frequency), amplitude, stator diameter, and tooth height of the ultrasonic motor, and the friction torque is closely related to the friction torque. Material, coefficient of friction and pre-stress.

Ultrasonic motor design requirements are generally its rated output power, that is, output a certain torque at a certain speed. In addition, the overall optimization goal of the ultrasonic motor is often to achieve the highest efficiency while meeting the design requirements. However, it should be noted that the local optimization objectives of each functional module should be clearly defined, and the mutual influence between modules should be considered as much as possible. This is especially important when the overall mathematical model of the ultrasonic motor is not yet perfect.

Initially select the parameter range, perform variable parameter analysis, analyze and determine the optimization parameters, and perform performance prediction based on the simulation model.

Adjust the parameters to get the optimal solution.

According to the module division of the ultrasonic motor power system, in order to obtain good dynamic characteristics of the ultrasonic motor, the stator resonant module and the friction drive module are mainly optimized to design the stator and the friction interface.

The main function of the stator of the ultrasonic motor is to generate resonance under the excitation of the induced strain of the piezoelectric ceramic, so as to effectively convert the electrical energy into mechanical energy and save it as vibration energy. Therefore, the key to optimal design of the stator is how to ensure the maximum degree of conversion of the electromechanical coupling energy within the range of the parameters that can be selected under the premise of satisfying the design requirements. Therefore, the stator mode, material, size, and piezoelectric ceramic should be used for this purpose. Several other aspects were considered. The design of the friction interface mainly includes two aspects, one is the selection of the friction material, and the other is the selection of the size of the friction layer and the pre-pressure.

In this paper, the damping loss, electromechanical coupling coefficient and vibration velocity (implicit amplitude and pre-pressure) of the stator vibration are used as evaluation indicators. The three are combined as the stator optimal design goal; the friction interface power loss is used as the friction interface optimization. The goal of design. The main purpose is to obtain better efficiency and friction drive performance while meeting usage requirements.

The design example and performance analysis of the 4-wave ultrasonic motor shows the stator and its operating mode of the ultrasonic motor applied to the valve developed by the China Southern Airlines Ultrasonic Motor Research Center. The parameters are shown in the following table. .

545 Type Valve Ultrasonic Motor Stator Structure and Operating Modes Model 545 Air Valve Ultrasonic Motor Stator Structural Parameters External Diameter Operating Mode Internal Diameter Operating Frequency Stator Base Thick Stator Material Steel Gear High Voltage Electric Ceramics Piezoelectric Ceramic Thick The motor is The prediction results of the change trend of the no-load speed and the stall torque under different pre-stresses are shown as the output power, the sliding loss power, and the friction interface efficiency curve of the ultrasonic motor friction interface under different pre-pressures. There are many diagrams for analysis of optimization design details obtained from the design program. Due to limited space, we will not list them here. For details, see the text when analyzing and designing the parameters of the ultrasonic motor. It is found that choosing the B7 mode shape is more appropriate. The frequency of this mode of operation is 36. The amplitude (at no preload) is 2 Lm, and the electromechanical coupling coefficient and the evaluation index are all relatively high. Through the analysis of its output characteristics, we find that the pre-pressure can be selected as 100N. At this time, the stall torque is 0.16Nm, and the idle speed is 140r/min. The corresponding distance D is slightly smaller than zero, which can ensure good contact with the stator and rotor. Without causing a large friction loss, the working point can be selected with a load torque of 0.1 Nm and a rotation speed of 90 r/min. At this time, the transmission efficiency of the friction interface can be no-load speed and locked-rotor torque of the 545-type valve ultrasonic motor. The changes of the ultrasonic motor friction interface in different pre-pressure output characteristics 5 conclusions of the ultrasonic motor performance simulation analysis software, can predict the ultrasonic motor at the design stage of the output characteristics.

The dynamic characteristics description index of ultrasonic motor is defined, and the variable parameter simulation analysis is performed, and the trend and sensitivity of each index with parameters change can be calculated.

Some theoretical principles for the optimal design of ultrasonic motor were proposed. Based on the simulation results of the dynamic characteristics, the basic methods for the optimal design of the stator dynamic characteristics and the friction interface transmission characteristics were proposed, and constructive suggestions were made for the optimization of the design parameters.

Ultrasonic motor dynamic simulation study has played a very good guiding role in optimizing the design. Based on this, the ultrasonic motor performance simulation analysis software developed in the research and development of rotary traveling wave ultrasonic motor plays an auxiliary analysis and design role. The effect is very significant.

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