机械专业毕业设计外文翻译外文文献.docx

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1、机械专业毕业设计外文翻译外文文献 A Multi-DOF Ultrasonic Motor Using In-plane Deformation of PZT Elements and Its Driving Circuit Minghui Zhang, Mantian Li and Lining Sun Robotics Institute Harbin Institute of Technology Harbin, Heilongjiang Province, China peterzmh Abstract - Due to the increasing number of DOFs of

2、 systems and the reducing the volume and weight of the devices, multi-degrees-of-freedom (DOF) actuators have become more useful in the field of robotics. And the general features of ultrasonic motors are also suitable for constructing a direct-drive multi-DOF actuator. So, a new multi-DOF ultrasoni

3、c motor using in-p lane deformation of PZT elements is introduced in this p ap er. Then its working p rincip le and requirement for driving circuit are analyzed. At last, a driving circuit is p rop osed accordingly which generates sinusoidal actuating signals with a FPGA part (a Direct Digital Synth

4、esizer (DDS) array is synthesized in it) and amplifies them with high voltage power operational amplifiers. It is characteristic of indep endent adjustment of amp litude and frequency for each outp ut signal and indep endent adjustment p hase between any two of outp ut signals. The circuit meets the

5、 requirement of the motor. Index Terms - ultrasonic motor; multi-degree of freedom; in-plane deformation; driving circuit I.I NTRODUCTION Multi-DOF ultrasonic motor is a new kind of multi-DOF actuator. With it or other multi-D OF actuators, dexterous multi-DOF can be generated easily, and at the sam

6、e time the volume and weight of the devices are also reduced greatly. And comparing to other multi-D OF actuators, multi-D OF ultrasonic motors can be easily miniaturized. Whats more, they also have many other excellent characteristics such as high torque at low speed, high stationary limiting torqu

7、e, absence of electromagnetic radiation, less noise, and simplicity of design. Some of the characteristics assure capability of ultrasonic motors as multi-DOF actuators, usable as direct-drive actuators. Especially, a multi-D OF ultrasonic motor with compact stator and simple driving circuit is very

8、 suitable for robot eye control, laser handling, and other applications 1. Therefore, many multi-D OF actuators based on the principle of ultrasonic motors have been proposed in the past. Toyama developed a spherical ultrasonic motor in which three or four ring-shaped vibrators are arranged around a

9、 spherical rotor 2. Takfumi designed an ultrasonic actuator with multi-degree of freedom using bending and longitudinal vibration of a single stator, which has been applied in an auditory tele-existence robot 3, 4. Takemura proposed a bar-shaped ultrasonic motor capable of generating three-DOF motio

10、n and a plate type multi-D OF ultrasonic motor whose rotor was larger in the size of volume 5, 6. Otokawa constructed an arrayed-type multi-DOF ultrasonic motor based on a selection of reciprocating vibration modes 7. Almost all these multi-D OF ultrasonic motors generate vibration by expanding and

11、contracting with the coupling commonly associated with the piezoelectric d33 (strain) or e33, (stress) coefficients. In order to obtain the optimum working character, a driving circuit for the ultrasonic motor should be developed. And to study the multi-D OF ultrasonic motor directly and easily, it

12、is better that the driving frequency and voltage of the output signal must be adjustable, and the phase between the outputs should also be controllable 8, 9. Takemura have proposed a self-oscillation driving circuit for the plate type multi-D OF ultrasonic motor they developed. Experimental results

13、confirm the rotor can be rotated using the self-oscillation driving circuit and the maximum rotational speed of the rotor is about 70 rpm 6. And King Long has also designed three kinds of driving circuits for a three-degree freedom of spherical piezoelectric ultrasonic motor 10. In this paper, a new

14、 multi-D OF ultrasonic motor is introduced, which generates vibration with the coupling associated with the piezoelectric d31 (strain) or e31, (stress) coefficients and the piezoelectric d15 (strain) or e15, (stress) coefficients. Then, a special driving circuit based on DDS is developed. The sinuso

15、idal driving signals are generated from the DDS array synthesized a FPGA part and amplified by high voltage power operational amplifiers. The frequency and amplitude of the four output signals from the driving circuit are all adjustable independently; and the phase between any of them can also be ad

16、justed. II.S TRUCTURE A ND P RINCIPLE A. Structure of the stator A square beam has two bending modes whose resonance frequencies are equal to each other. And with calculated dimensions, it may have one longitudinal mode which is orthogonal to them and its resonance frequency also corresponds to them

17、. The second bending mode frequencies in any direction for circular cylinders are equal to each other and the first longitudinal mode frequency can be very close to them. The stator of the motor presented in this study combines the circular and square cross sections. The outside surface of a hollow

18、metal cylinder is flattened on four sides at 90 degrees to each other and four rectangular piezoelectric plates are bonded onto these four flattened Proceedings of the 2022 IEEE International Conference on Mechatronics and Automation August 5 - 8, 2022, Harbin, China surfaces Fig. 1. The PZT plate h

19、as five electrodes; four are deposited on the top surface while the fifth one is deposited on the bottom surface of the PZT plates. On the top of PZT plates, two electrodes are connected across corners as one input, and the inputs on the symmetric positions of the stator are defined as one input ele

20、ctrode group. And the bottoms of PZT plates are electroded uniformly and they are ground. With the application of an alternating current (AC) voltage potential across the thickness of the piezoelectric plate, the plate will expand and flex due to the coupling commonly associated with the piezoelectr

21、ic d31(strain) or e31, (stress) coefficients and the piezoelectric d15(strain) or e15, (stress) coefficients 11, 12. With the configuration shown, the plate deforms in-plane and makes longitudinal and bending vibration of the base. (a) (b) Fig.1 Structure of the stator. (a) orthographic view ; (b) t

22、op view B. Vibration modes Fig. 2 shows the driving principle of the multi-D OF ultrasonic motor. The rotor can rotate around three perpendicular axes. A longitudinal vibration and two bending vibrations of the stator are used as shown in Fig. 2. Fig. 2(a) shows the natural vibration modes of the st

23、ator that are used when the rotor rotates around the z axis. Figs. i and iii show the second bending mode of the stator in the x-z plane (mode A), and Figs. ii and iv show the second bending mode of the stator in the y-z plane (mode B). When these two natural vibration modes, A and B, are combined a

24、t a phase difference of 90, the tip of the stator rotates around the z axis. Then, the spherical rotor in contact with the stators head also rotates around the z axis by frictional force. Fig. 2(b) shows the natural vibration modes used when the rotor rotates around the x axis. Figs. i and iii show

25、the first longitudinal mode of the stator along the z axis (mode C), and Figs. ii and iv show the mode B. when an electrical excitation is imposed between electrode group A or B and ground, these two natural vibration modes, B and C, are combined at a phase difference of 90, and the tip of the stato

26、r rotates around the x axis. Then, the spherical rotor also rotates around the x axis due to frictional force. Excitation of input electrode group A and ground will cause the counterclockwise rotation by right-hand rule, while excitation of input electrode group B and ground will cause the clockwise

27、 rotation. The rotor rotates around the y axis when the mode A and the mode C are combined in the same way as the case of Fig. 2(b). The point to notice is that the natural frequencies of these three natural vibration modes, A, B, and C, should be as close as possible. Table I shows the input phases

28、 for the PZT plates needed for excitation each rotation. (a) (b) Fig.2 Driving principle of the multi-DOF ultrasonic motor. (a) around z axis; (b) around x axis When a driving voltage is applied on electrodes A1 and A2, vibration modes B and C can be excited the same time. Accordingly, the tip of th

29、e stator rotates around the x axis counterclockwise. Then, the spherical rotor in contact with the stators head also rotates around the x axis counterclockwise by frictional force. Similarly, the spherical rotor rotates around the x axis clockwise, when a driving voltage is applied on electrodes B1

30、and B2. And the excitation on electrodes C1 and C2 will cause the counterclockwise rotation of the rotor and he excitation on electrodes D 1 and D 2 will cause the clockwise rotation of the rotor, as well. The rotor will rotate around z axis counterclockwise with electrodes A1 and C1 being excited s

31、imultaneously at a phase difference of 90 and rotate around z axis clockwise with electrodes B1 and D 1 being excited simultaneously at a phase difference of 90 . C. Geometry Since the design is complicated, finite element analysis method is used to conduct modal and harmonic analysis of the ultraso

32、nic motor, including the linearized piezoelectric material properties. In this way, a feasible design can be developed from the concept with reasonable assurance that the results of the analysis would resemble the behavior of an actual actuator. Fig. 3(a) and (b) show the calculated first longitudin

33、al mode and the calculated second bending mode of the stator, respectively. The calculated natural frequencies of these modes are very close, about 57 kHz Table I. (a) (b) Fig.3 Vibrating modes of stator. (a) second bending mode; (b) first longitudinal mode TABLE I N ATURAL F REQUENCIES O F T HE S T

34、ATOR Vibrating mode Natural frequency (KHz) First longitudinal mode along z axis (L1) 56.7 Second bending mode in the x-z plane (B2) 56.6 Second bending mode in the y-z plane (B2) 56.6 The basic configuration of the motor is shown in Fig. 4. The rotor is made of stainless steel. The stator of the pr

35、ototype motor consists of a hollow metal tube (brass) with an outer diameter of 10 mm and inner diameter of 6 mm, length of 16 mm, and four rectangular piezoelectric plates with dimensions, 16 mm in length, 8 mm in width, and 1 mm in thickness. The outside surface of the metal cylinder is on four si

36、des at 90 degrees to each other. The PZT plates (PZT4, Kunshan Jingfeng Electric Corp., Ltd.), which are poled in the thickness direction, are bonded onto to the flat orthogonal surfaces of the cylinder using a conductive epoxy Fig.1 (b). The stator is held on the base with four screws. And the supp

37、orting points are on the nodal plane. Fig.4 Assembly diagram of MDOF USM III. D RIVING C IRCUIT A. Structure For driving ultrasonic motors, a generation of the desired natural vibration of the stator is one of the most important points. Considering the requirement for excitation of each rotation, we

38、 propose a driving circuit for multi-D OF ultrasonic motors which can generate four independent alternating excitation signals. The amplitude and frequency of each signal can be adjusted individually; the phase between any two of the four excitations can be adjusted individually, as well. Fig. 5 sho

39、ws the schematic diagram of the driving circuit. The circuit includes the D SP controller, the FPGA part in which a D D S array are synthesized, D /A modules, low pass filters (LPF) and power amplifiers (PA). The DSP controller receives commands, encoder values and other feedbacks, and then controls

40、 the digital potentiometer and the FPGA part correspondingly. The D SP controller communicates with the FPGA part through a dual port RAM. The frequency and phase information for each output is written in RAM by DSP controller and read by the FPGA part which uses it as the parameter for the D D S ar

41、ray. The four D D S modules in the D D S array generate the four excitation outputs respectively. Actually, the output signal of DDS module is coded sinusoidal signal, and must be transformed to step sinusoidal wave by D/A module and smoothed by low pass filter. After amplified by the power amplifie

42、r, the smooth ultrasonic sinusoid wave serves as the excitation signal. Fig.5 Schematic diagram of the driving circuit B. Working principle Since the output voltage of the D /A module is proportional to its reference voltage and the amplitude of the driving circuit output is also proportional to the

43、 output voltage of the D/A module, the amplitude of the driving circuit output can be adjusted by setting the reference voltage of the D /A module. D igital potentiometers are used to modify the reference voltage. All digital potentiometers get their values from the DSP controller and update the val

44、ues simultaneously with the unique chip select signal. The adjustment of the frequency of the outputs and phase between outputs is realized by D D S and described as the follows. Fig. 6 shows the schematic diagram of a DDS, where K is the frequency control word, f c is the frequency of the input clo

45、ck signal, N is the digital capacity of DDS. At every rising edge of input clock, the accumulator accumulates in step length of K . The output of accumulator is added with P and its result acts as the address of the wave pattern ROM. All the information of wave is stored in the ROM. The output of RO

46、M is turned into step wave in D /A converter 13. After passing the low pass filter, the step wave is smoothed and all the harmonic components are removed. In the D D S system, the accumulator, the adder and the ROM in the imaginary line block are synthesized in FPGA, while others parts are individua

47、l electrical components. The frequency of the DDS output signal is: K f f N c out 2 where f out is the frequency of the output. The frequency is in ratio of the frequency control word K , so f out can be adjusted proportionally by changing the value of K . Thus the frequency range of DDS output is from f c /2N to f c /2, when the frequency control word is in a span from 1 to N-1. But in order to guarantee the output accuracy, there at least need to be four sampling points in one period. The maximum of K is N-2, that