Using the inverse piezoelectric effect of piezoelectric materials, that is, under the action of an alternating electric field, the piezoelectric material will produce a telescopic phenomenon. Through the conversion and coupling of various stretching vibration modes, the electric energy is directly converted into mechanical vibration energy, and the friction is utilized. Turn into a rotating or otherwise moving drive. Compared with the electromagnetic type motor, it has the following features: 1 Compact and simple structure, can be embedded according to the requirements of the drive structure, can be integrated with the system, such as Canon camera automatic zoom lens, the motor is two stator ring, can be with the lens Integrated together, through the middle of the ring through the light; 2 energy density is 5 times that of the electromagnetic motor, is a typical low-speed high-torque motor, can be used for direct drive, thus reducing the weight of the flying object, for the aerospace field, Also suitable for space special environment; 3 easy to adjust speed, low-speed smooth and no pulsation, but in the control and can achieve stepping drive, and high positioning accuracy, 4 after power failure has friction self-locking function, and due to vibration in the high frequency domain The energy decay is very fast, and it has very high dynamic response (mechanical time constant within several ms), so it is easy to realize high-precision speed and position servo control; 5 The clearance generated by the gearless reduction device can be accurately positioned; Similar to the DC motor torque droop characteristics; 7 Because there is no core and coil, so strong anti-electromagnetic interference, that is electromagnetic compatibility (EMC Pregnancy inadequacies are: 1 relatively high manufacturing costs, but the cost can be greatly reduced when mass production; 2 due to friction driven, friction material life problems will affect the working life of the motor, the current traveling wave ultrasonic motor continuous The operating life has reached 600 Ch, longitudinal torsional composite ultrasonic motor is already in place. The two PZT oscillators of the hybrid ultrasonic motor respectively excite two forced vibrations that are perpendicular to each other and have the same frequency, and the two vibrations can be individually adjusted. The torsional vibration generated by the torsional vibrator is used to drive the output torque of the rotor, and the axial vibration is generated by the longitudinal vibrator to control the friction between the stator and the rotor to convert the alternating torsional vibration into a single-direction rotary motion of the rotor, and the process is similar to the rectification. According to the similarities and differences between the torsional vibration and the direction of motion of the rotor, the motion of the hybrid ultrasonic motor during one vibration cycle can be divided into two processes: the direction of torsional vibration (2) (3), the direction of torsional vibration and the direction of rotation of the rotor. In the same way, the longitudinal vibration is elongated in the axial direction, and the axial displacement is shown by the arrow. The stators and rotors are in close contact with each other, and the torsional vibration of the stator elastic body is transmitted to the rotor through friction coupling to drive the rotation of the rotor. In the negative half cycle of the torsional vibration (3h ( 1) The direction of torsional vibration is opposite to the direction of rotation of the rotor, and the direction of longitudinal vibration is opposite to that of the front half, shortened along the axial direction, and the stator and rotor are quickly detached, due to the superimposed effects of vertical and torsional vibrations in the positive and negative half cycles, A one-way rotating motion of the rotor is formed.This ultrasonic motor is characterized by the ability to independently change the torsional piezoelectric ceramic The drive voltage of the sub-stacked piezoelectric ceramics controls the vibrational trajectory of the surface particles, which enables the motor speed and steering to be well controlled, and the low-speed operation is stable, since the torque is generated by a separate vibrator, in particular the stator-rotor intermittent contact Drive, it is easy to achieve low-speed large torque output 2 motor structure and tuning of the longitudinal torsional composite ultrasonic motor requires the same action as the longitudinal torsional vibration, in order to make the amplitude of both vibrations are larger, the motor works in the resonance point of longitudinal torsional vibration or Close to the resonance point, it is necessary to make the longitudinal and torsional vibration resonance points of the motor structure be the same or close to each other. This is the tuning problem of the longitudinal-to-twist compound ultrasonic motor, but the longitudinal and torsional vibrations are caused by the different acoustic transmission speeds of the longitudinal and torsional vibrations in the stator. The resonant frequency is different. For equal section stators, the resonant frequency of the same order is longer than the torsional vibration, which is generally 1.6 times. In addition, it is difficult to use the high order frequencies of the vertical and torsional oscillators. Because the frequency is high, the amplitude of the stator surface is very high. Small, making the rotor unable to extract the stator vibration energy through the frictional contact surface, so the first developed motor, which works in the torsional oscillator At the order of the resonant frequency, the longitudinal vibrator has a large longitudinal vibration amplitude 181 through the laminated piezoelectric stack. However, the piezo stack is difficult to bond and has a problem of strength due to the shear force. Therefore, it is natural. It is proposed to use the stator as a longitudinal vibrator (also a torsional oscillator), and the rotor as a torsional oscillator (or longitudinal vibrator) whose stator and rotor can be designed based on the working frequency. This type of motor requires a relatively complicated structure because the rotor needs brush conduction. And the energy of bookmark1 of the prototype is concentrated to a point or a small part (usually the diameter of the top of the horn is much smaller than the diameter of the piezoelectric slice). Similarly, the stator stepped shaft structure is used to reduce the longitudinal vibration frequency and increase the torsional frequency. Therefore, the shaft diameter of the stator surface is smaller than the diameter of the piezoelectric film, which increases the rotation speed of the motor, but reduces the torque of the motor. For the ultrasonic motor to obtain large torque, it is necessary to transfer the vibration energy to the large ring. It is also a method to adjust the frequency of longitudinal vibration through the weight, but the mass gain of the system P. The external diameter of the stator structure we proposed is consistent with the piezoelectric film, and the internal is the hollow variable. The surface structure, as shown, not only allows the resonance frequency of the longitudinal torsional vibration to be close, but also increases the position of the longitudinal torsion piezoelectric film in the torsional amplitude stator. This has a great influence. In the past, the longitudinal torsion piezoelectric film was installed in the The vibration of each stator in the stator, but due to the influence of the motor rotor pressing force and rotor load, the effect is not good, the actual vibration coupling should be considered under the coupling of the stator and rotor, due to a large number of factors, we must completely sort out There is a certain degree of difficulty, but can be estimated based on the equivalent parameter method, from the perspective of the mutual analysis of the stator and rotor and the impact of the load and other aspects of consideration. On the other hand, from the PCL-818 data acquisition card, the card has I / O function interface And three timers/counters are available. From the test results, the transient process is consistent with the theoretical analysis. The transient characteristics during load are just as described above, measured by the large voltage (the high current measured and the small frequency current sweep have a certain access, using HP4192 The first-order resonance frequency of the torsional vibration obtained is 4 kHz, which should be determined by the large current. The first-order resonance frequencies of the longitudinal torsional vibration are 223 kHz and 20.5 kHz, respectively, and the two are very close to each other with a difference of only 1.1 times, which indicates the aforementioned design. The method and the use of a hollow variable cross-section structure are relatively successful. It can be seen from the experiment that the torsional oscillator has an anti-resonance point, while the oscillator does not have a fundamental oscillator. The frequency change has different effects on the longitudinal oscillator and the torsional oscillator. The frequency change has a greater influence on the longitudinal oscillator, and the voltage of the vertical vibration changes significantly, which depends on the demand of the torsional oscillator.
Among them, the one-chip computer system is mainly responsible for the on-off between the small signal produced by the signal generator to the power amplifier, and the PC should be thrown away, and the sound in the text is smaller. In addition, the increase of the fixed rotor compaction force helps to increase the resonant frequency of the longitudinal torsional oscillator. From the view of the operating frequency of the motor, the working frequency of the longitudinal-twist compound ultrasonic motor is very wide, from about 25.4 kHz to about 7 kHz. The operating frequency range is stable, but the mechanical characteristics are best near the resonant frequency of the torsional oscillator. This shows that although the operating frequency of the longitudinal-twisted composite ultrasonic motor is very wide, it is still necessary to select a suitable operating frequency to obtain better operating characteristics. The actual operating frequency of the motor is selected in the range of 20 to 21 kHz, at which time the motor operates at resonance ( Torsional) and non-resonant (longitudinal oscillator) point operation, but the amplitude of the longitudinal vibration is still large at this time, so there is a large torque output. 7 High-precision stepping positioning control strategy Ultrasonic motor has strong nonlinearity, it is difficult to establish its Control model, the traditional electromagnetic induction motor positioning control method is not appropriate rejection In addition, most of the ultrasonic motor driver signal generator part does not have program-controlled interface, mostly fixed parameters or manual adjustment, even if there is a program-controlled interface, such as serial Communication is also not suitable for real-time control. Therefore, it is of practical significance to study a control strategy method that requires low control accuracy for the control circuit. For this reason, we propose a stepping positioning control strategy and a stepper motor to give a constant angle to a pulse signal ( Its size is determined by the structure of the motor.) When an ultrasonic motor gives it a sine wave (or square wave) When the number is activated, the motor can rotate through a certain amount of angle, but the size of the rotation angle depends on the performance and load of the motor, and it is difficult to measure the rotation angle. However, if N sine waves or square waves are sent continuously at one time, the ultrasonic wave The motor will rotate forward through an angle. If you continue to send N waveforms, the motor will again turn through an angle. The mechanism is that during the time when N waveforms continue to be sent, the motor accelerates in accordance with the starting characteristic curve, and after shutdown, the shutdown characteristic curve drops to stop. At this time, the area surrounded by the start-up and shutdown characteristic curves is the stepping of the motor. "Angle" experiments show that when the motor's running characteristics are stable and the load is constant, the running step of the motor is relatively uniform, but its step angle is directly related to the load characteristics. Due to the reduced speed under load, its "step angle" Also smaller. The experimentally measured no-load and load acoustic motor is used as a stepper motor, but for ultrasonic motors, the so-called “step angle†is variable, related to wave number and load, so that in order to achieve precise positioning of the motor, The time interval between step and step in the stepping positioning control strategy can be used properly. Too short motor will produce noise, if it is too long, the accurate positioning time will be prolonged. It is necessary to calculate the rotation angle of the ultrasonic motor according to the actual responsibility, and according to The algorithm gives instructions to the microcontroller. The basic idea of ​​the control algorithm is as follows: According to the positioning requirements, the operating position of the motor is divided into three categories: 1. Not close to the required position; 2. Close to the required position; 3. Has reached the required position. In the first case, the motor runs continuously. When the second case is reached, the motor changes from continuous operation to step operation until the third condition stops operating. Obviously, there are two important parameters that need to be set. The first parameter is when the approaching target is changed to a single step and there is an advance, because there will be a shutdown corner during the electrical shutdown process, and the advance must be greater than the shutdown rotation, but It is also necessary to approach the two. In this way, the positioning time is short. The second parameter is the number of wave N per step. The larger the step angle is, the lower the positioning accuracy is. The smaller N is, the longer the positioning time is, and the higher the positioning accuracy is. In addition, when choosing N, we must also consider that the average positioning error is close to zero. This can be determined experimentally. In the test system, single-step operation is independently controlled by the single-chip microcomputer. The count of N is determined by the single-chip timing counter and the continuous and single step of the motor. The stop command communicates with the I/O port of the microcontroller through the I/O port of the PC industrial control card. The instruction time is generally a few microseconds, which is much less than the period of one signal wave (the drive frequency is 20kHz, ie, the period is 50 microseconds). Therefore, fully meet real-time control requirements from 0.01° to any size. Table 2 shows the experimental results when the positioning requirement is 90°, and the experiment is repeated 100 times. The parameters are as follows: 0.15° in advance is equivalent to 30 pulses. Positioning accuracy is better than 0.02° is equivalent to 4 pulses. N is taken as 100 5010 and 3. Obviously, the step size has a greater influence on the positioning accuracy. Therefore, the number of wave numbers N per step can be reasonably selected according to different positioning accuracy requirements. For this system, the above control method can realize 0.005° 1 pulse), which is also the minimum resolution of the test system. If the resolution of the photoelectric encoder can be improved, the control accuracy can also appropriately improve the positioning accuracy of the different N of Table 2. Test Results Number of Experiments 100 耜 Minimum Value Error Range Measure Mean 8 Conclusion This paper presents a prototype of a low-speed, high-torque longitudinal-twist compound ultrasonic motor for aerospace applications. The results show that it has the advantages of mass/low low-speed high torque and fast response. The transient process can be approximated as a first-order lagging link, which is very suitable as a high-grade control motor. It is suitable for aerospace feasible transient characteristics testing methods and high-precision stepping positioning control strategies to promote the application of ultrasonic motors in aerospace engineering. Must focus on the improvement of efficiency, quality reduction and the reliability of space environment, further study the new structure and optimize the structure, and deepen the drive control power supply, especially the adaptive research of the space environment, the experiment of the space, natural and mechanical environment of the motor, etc. To further improve the understanding of the applications of ultrasonic motors in aerospace applications
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