Ultrasonic linear actuator using coupled vibration

Transcription

1 J. Acoust. Soc. Jpn. (E)11, 4 (1990) Ultrasonic linear actuator using coupled vibration Kazumasa Ohnishi* and Kenjyo Yamakoshi** Niigata Division, ALPS Electric Co., Ltd., 1-3-5, Higashitakami, Nagaoka, 940 Japan Toyama National College of Technology, 13, Hongo-cho, Toyama, 939 Japan (Received 25 September 1989) Recently many researches and developments have been intensively made on ultrasonic actuators, because of their merits such as compactness, simple structure, and high re sponsewith controllability. For the realization of ultrasonic actuator, the edge of actuator with elliptic or oblique locus is needed. Recently, the authors have devised a new driving principle of ultrasonic actuator. By this principle, the coupled vibration of longitudinal vibration and flexural vibration excited by non-linear joint of the bars. According to the devised principle, a vibrator was manufactured using multi-layered piezoelectric actuators and aluminum bars. By the LDV method, the vibration locus of the vibrator edge was confirmed to be elliptic. The operation characteristics of the ultrasonic linear actuator was measured as ca. 30 cm/s at the driving voltage of 15 V. Keywords:Ultrasonic, PACS number:43. Linear, Actuator, Piezoelectric, Vibration 35. Ty, Yb 1. INTRODUCTION The actuators using high power ultrasonic wave have been widely studied up to date. 1-7) However, among them, only rotary type has been developed for practical use, for example for the autofocussing mechanism of cameras.8) Similarly, for linear type also, the travelling wave method has been studied, 9) but so far been unsuccessful in practical application. This can be attributed to the necessity of larger scale vibration system with low efficiency. In the present paper, a novel ultrasonic actuator for which the performance with smaller size and higher efficiency is expected, is reported. The operation method of the actuator uses the coupled vibration of longitudinal and flexural vibra tionswhich is yielded by non-linear connection of bars (hereafter will be called Connected Bar Actuator Method). Its operation principle is described in terms of equation of motion and FEM, and the operation characteristic of the ultrasonic linear actuator manufactured using multilayered piezo electricactuator 10) and aluminum bars is also re ported. 2. CONSTRUCTION In the ultrasonic actuators which have been put for practical use, the travelling wave method is used, its movement being of rotary type. On the other hand, that of linear type by any method has not been developed for practical use. The linear motor by travelling wave the method is operated by the principle shown in Fig. 1. In other words, when a travelling wave is propagated through an elastic material, every particle on its surface vibrates with elliptic locus. Then, at the crest of the vibration perpendicular to the surface, the par ticlealways possesses a velocity component parallel to the surface. Therefore, if a movable object is pressed against the crest, it obtains a propulsive force along the direction of the arrow in Fig. 1, through the frictional force at the crest of the wave. The construction of the practical vibration system using this principle consists of the longitudinally 235

2 J. Acoust. Soc. Jpn. (E) 11, 4 (1990) Fig. 1 The principle of the ultrasonic motor. Fig. 2 The principle of the ultrasonic linear motor using the travelling wave. Fig. 3 Construction of vibrator. vibrating points at the both edges of the transmitting bars (Fig. 2), where the travelling wave is generated at one edge, while it is accepted at the other. By switching the generating edge and the acception edge, the propagation direction of the flexural wave can be reversed. However, this construction re quiresthe excitation of the travelling wave through outthe whole transmitting bar, which implies that the longer the moving distance is, the larger the scale of the vibration system required and the lower the efficiency as a motor becomes, respectively. The construction of the ultrasonic linear actuator deviced in the present study is illustrated in Fig. 3. One edge surface of aluminum, an elastic material is making an angle of ľ with respect to its central Fig. 4 Construction of ultrasonic linear actuator. axis, where a multilayered piezoelectric actuator is connected. For the connection, a polymer ad hesiveis employed. On the other hand, the opposite edge surface of the aluminum rod which is perpendic ular to the central axis contracting the rail is at tachedwith a friction material with the polymer adhesive. A polyimide composite material is used as the friction material. The friction material is employed for the purpose of both minimizing the wear of the bar and increasing the friction between the bar and the rail. In Fig. 4 is shown the construction of the ultra soniclinear actuator. The vibrator is fixed to the case with a bolt near its joint. And in order to intensify the friction between the rail and the vibra tor,the load is charged by pressing the vibrator against the rail from the bottom side of the rail through rollers by the aid of springs. The material for the rail is iron (S45C), while the surface rough nessis about 3S. 3. OPERATION PRINCIPLE The coupled vibration of longitudinal and flexural vibrations is excited non-linear connection of bars. The operation principle of an ultrasonic linear using this type of vibration is illustrated step-wise in Fig. 5, which is explained as follows: (1) No displacement with the piezoelectric ele mentnor the elastic material. (2) Both the piezoelectric element and the elastic material are elongated and bent toward the left side. (3) No displacement with the piezoelectric element nor the elastic material. (4) Both the piezoelectric element and the elastic material are shortened and bent toward the right side. where, the piezoelectric element is a multilayered type piezoelectric actuator, while the elastic material being aluminum bar. The outline of the linear 236

3 K. OHNISHI and K. YAMAKOSHI:ULTRASONIC LINEAR ACTUATOR Table 1 Symbol list. Fig. 5 Motion of ultrasonic linear actuator. <Equations with Bar A> Longitudinal vibration: Fig. 6 Connected bars. actuator is as above described, but the elongation/ shortening and the flexural displacement varies with driving frequency. The actuator vibrates with a period corresponding to the cycle (1) (2) (3) (4) In the next, the coupled vibration of the longi Flexural vibration: tudinalvibration and the flexural vibration is ex pressedby differential equations. The non-linear connection of the bars is given in Fig. 6. According to the evaluation of Timoshenko's equation by Miklowitz,11) the frequency equations of the coupled vibration of the longitudinal and the flexural vibrations excited by the non-linearly con nectedbars are solved. The notation of symbols have been given in Table 1. <Equations for bar B> Longitudinal vibration: 237

4 J. Acoust. Soc. Jpn. (E) 11, 4 (1990) Flexural vibration: From the above equations, the following matrix is obtained. The frequency equation is given by assuming that From the general solutions derived above, the solu tionswhich satisfy the following conditions are sought. Namely, from the boundary condition at the edge A: Similarly, from the boundary condition at the edge B: the determinant of the above matrix [ƒ ij] is equal to zero. Subsequently, a FEM program suitable for the vibration analysis of square bar, plate etc. was developed in order to analyse the vibration of the bars in the present case. In the analysis of flexural vibration, use of first order element generally cases poor precision. Therefore, effort was made to improve the approximation precision in the present study, by using second order function in xy-plane within triangle plate element. The displacement within the triangle plate element is given by (1) where, f1e,f2e,f3e are the second order functions of x,y, and the linear functions of z, respectively. The triangle plate element is illustrated in Fig. 7. Thus, assuming that the freedom of every con nectionis 5, and the parameters ux, uy, uz, ƒæx, and ƒæy, On the other hand, from the boundary condition at the connection: were analysed. The kinetic equation of an elastic body in homogeneous media is given by Fig. 7 Triangle plate element. 238

5 K. OHNISHI and K. YAMAKOSHI: ULTRASONIC LINEAR ACTUATOR (2) where A and Đ are Lame's constants. By the developed FEM program, both kinetic and strain energies were calculated from Eq. (1) Also, the natural frequency calculated from the frequency equations, and those obtained by FEM are compared with the practical values measured for the manufactured actuator. As shown in Table based on Eq. (2) and plate vibration was analysed by general vibration analysis method. 4. RESULT OF TRIAL MANUFACTURE AND TEST The bars with material constants and dimensions given in Table 2 were non-linearly connected, and its natural frequency was measured by impedance analyser, of which the result is shown in Fig. 8. FREQ=30.9KHz Table 2 Data of connected bars. FREQ=78.9KHz FREQ=91.2KHz Fig. 8 Impedance by experiment. FREQ=131.5KHz Table 3 Natural frequency by experiment. [khz] FREQ=155.4KHz Fig. 9 Natural frequency and vibration mode by FEM. 239

6 J. Acoust. Soc. Jpn. (E)11, 4 (1990) 3, the three values show fairly good coincidence for each case, which clearly indicates that the vibration is a coupled vibration of longitudinal and flexural vibrations. The vibration modes for respective natural frequency, which have been analysed by FEM, are illustrated in Fig. 9. In the next, the characteristics of the manufactured ultrasonic linear actuator with the construction shown in Fig. 4 was measured. First, the relation between driving frequency and moving direction was observed, of which the result is given in Fig. 10. The observed variation of the moving direction by frequency suggests that the phase discrepancy be tweenlongitudinal and flexural displacements varies with the driving frequency. Secondly, the dis placementof the driving plane as a function of the driving frequency was measured employing the LDV. The measuring point was the center of the driving plane. Along X and Y directions, the LDV for longitudinal vibration and that for planer velo citywas used, respectively. The result is shown in Fig. 11. The moving direction shown in Fig. 10 can be explained from the phase discrepancy be tweenx and Y directions. Thirdly, the relation between the driving voltage and the velocity of the ultrasonic linear actuator is illustrated in Fig. 12. The loaded weight was 3 kg, while driving frequency being 115 khz. For ex ample,its velocity reaches to more than 30 cm/s for the driving voltage of 15 V. On the other hand, the load-velocity curve is given in Fig. 13. The maximum load was about 350 g, above which the load caused the stop of the actuator. From this relation, the efficiency was obtained. The result is shown in Fig. 14, where the efficiency shows its maximum value at the load of ca. 200 g. Fig. 12 Voltage dependence of velocity of the ultrasonic linear actuator. Fig. 10 Driving frequency vs. moving direc tion. Fig. 11 Driving frequency vs. Phase. Fig. 13 Load dependence of velocity of the ultrasonic linear actuator. 240

7 K. OHNISHI and K. YAMAKOSHI:ULTRASONIC LINEAR ACTUATOR 6. PROBLEMS LEFT FOR FUTURE 1 ) The construction design for higher efficiency. 2 ) The design of the construction that gives the equal speed and driving force for the both moving directions. Fig. 14 Load dependence of efficiency of the ultrasonic linear actuator. 5. CONCLUSION An ultrasonic linear actuator operating by the coupled vibration of longitudinal and flexural vibra tionswas devised, manufactured and evaluated of its basic characteristics. 1 ) It was confirmed that the non-linear con nectionof a multilayered piezoelectric actuator and an aluminum bar excites a coupled vibration of longi tudinaland flexural vibrations, enabling the opera tionof a ultrasonic linear actuator. 2 ) The frequency equation of the non-linearly connected bars was solved and the obtained solution was proved to coincide well with the value measured for the manufactured actuator. By this fact, the operation principle of the actuator was confirmed. 3 ) The vibration of the non-linearly connected bars was simulated by FEM. The result shows a good coincidence with the observed result. From the vibration modes analysed by the FEM, it was also confirmed that the total vibration is the coupled vibration of longitudinal and flexural vibrations. REFERENCES 1 ) Y. Tomikawa, T. Ogasawara, S. Sugawara, M. Konno, and T. Takano,"On the construction of an ultrasonic motor," Paper of Tech. Group, IECE Jpn., US87-5 (1987)(in Japanese). 2 ) M. Kurosawa and S. Ueha,"An ultrasonic motor using a vibrator and multilayer piezoelectric actua tors,"paper of Tech. Group, IECE Jpn., US87-31 (1987)(in Japanese). 3 ) T. Takano, Y. Tomikawa, T. Ogasawara, S. Sugawara, and M. Konno,"Ultrasonic motors using piezoelectric ceramic multi-mode vibrators," Jpn. J. Appl. Phys. 27 (Suppl. 27-1), (1987). 4 ) K. Uchino, K. Kato, M. Imaizumi, and M. Tohda, "Ultrasonic linear motors using pie zoelectric actuators," J. Ceram. Soc. Jpn. 96, (1988)(in Japanese). 5 ) Y. Taniguchi, H. Shimizu, and T. Yoshida,"Im provementof ultrasonic motor using bar type bending vibrator," Proc. Spring Meet. Acoust. Soc. Jpn., (1989)(in Japanese). 6 ) Y. Tomikawa and T. Takano,"Equivalent circuit of an ultrasonic motor," Proc. Spring Meet. Acoust. Soc. Jpn., (1989)(in Japanese). 7 ) T. Takano and Y. Tomikawa,"Linearly moving ultrasonic motor using a multi-mode vibrator," Jpn. J. Appl. Phys. 28 (Supple. 28-1), (1989). 8 ) K. Hosoe, 1988 Symp. on Micro Motor Techniques, Tokyo, A2-2-1 (1988.3)(in Japanese). 9 ) M. Kuribayashi, S. Ueha, and E. Mori,"Excita tionconditions of flexural travelling waves for reversible ultrasonic linear motor," J. Acoust. Soc. Am. 77, (1985). 10 ) K. Uchino, PiezoelectriclElectrostrictive Actuators (Morikita Publishing Co., Tokyo, 1986)(in Japa nese). 11 ) Y. Watanabe, Y. Tsuda, and E. Mori,"A study of the flexural wave solutions for design of high power flexural vibrators," Proc. Autumn Meet. Acoust. Soc. Jpn., (1988)(in Japanese). 241