- Email: [email protected]
A novel dual stator-ring rotary ultrasonic motor
Sensors and Actuators A 189 (2013) 504–511
Contents lists available at SciVerse ScienceDirect
Sensors and Actuators A: Physical journal homepage: www.elsevier.com/locate/sna
A novel dual stator-ring rotary ultrasonic motor Xiaolong Lu, Junhui Hu ∗ , Lin Yang, Chunsheng Zhao State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics & Astronautics, Nanjing 210016, China
a r t i c l e
i n f o
Article history: Received 4 September 2012 Received in revised form 6 November 2012 Accepted 6 November 2012 Available online 16 November 2012 Keywords: Rotary ultrasonic motor Flexural mode traveling wave Dual stator-ring Bending mode Langevin transducers
a b s t r a c t In this work, a novel dual stator-ring rotary ultrasonic motor is proposed, designed, fabricated and characterized for raising driving torque of the rotary ultrasonic motor operating in the flexural vibration mode. It uses four bending mode Langevin transducers, which are evenly distributed between its two identical stator rings, to excite the ninth order flexural mode traveling waves in the two stator-rings and drive its two rotors. Driving bars assembled at the center of the Langevin transducers are employed to excite two ninth order flexural standing waves spatially and temporally orthogonal to each other in each stator-ring, and form the traveling wave. Results of vibration measurement are used to confirm the operating principle, and the finite element method is used to design the motor size in order that the motor can operate in resonance. The appearance size of the motor is 80 mm × 80 mm × 53 mm, stator outer diameter is 60 mm, and operating frequency is around 39 kHz. The major mechanical and thermal characteristics of the motor have been measured. At the room temperature and 250 V0-p operating voltage, its stalling torque is 1.6 Nm, no-load speed is 120 rpm, and output power reaches the maximum (=5.5 W) with a driving torque of 0.9 Nm and speed of 54 rpm. At ambient temperature of 100 ◦ C, the motor still has stalling torque of 0.9 Nm and no-load speed of 79 rpm for a operating voltage of 250 V0-p , which means that this motor can operate in relatively high temperature environment. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Ultrasonic motors have the merits of high torque to volume ratio, high positioning precision, intrinsic holding torque, compared to the conventional electromagnetic motors [1–4]. Recent applications of ultrasonic motors include space explorations, ultraprecision measurement, biomedical equipment, etc. [5–7]. In these applications, high adaptability to environment and high reliability of ultrasonic motors are desired. Some ultrasonic motors with bonded piezoelectric components have good performances [3,4,8–10], but the piezoelectric wafer may fall off from the bonding layer after a long time operation or during the operation in high temperature environment [5]. Comparatively, ultrasonic motors excited by Langevin transducers are more reliable and competitive in environment adaptability and working life [11,14]. There have been a lot of reports on the ultrasonic motors excited by Langevin transducers, many of which use longitudinal or bending vibration mode or both of them for vibration excitation. Kurosawa et al. [12] proposed an ultrasonic linear motor using two sandwich-type vibrators for large thrust applications. Satonobu et al. [13] proposed an ultrasonic motor with symmetric hybrid transducers. Iula and Pappalardo [14] proposed a
∗ Corresponding author. E-mail addresses: [email protected], [email protected] (J. Hu). 0924-4247/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.sna.2012.11.009
high-power traveling wave ultrasonic motor with several transducers. Liu et al. [15] proposed a square-type rotary ultrasonic motor with four driving feet. More research efforts in this area could be found in Refs. [16–18]. These motors can output large power but their dimensions are usually big. Research of ultrasonic motors with compact structure and excited by Langevin transducers is significant for practical applications. In this work, we have proposed and developed a novel dual stator-ring rotary ultrasonic motor, which is excited by four evenly distributed Langevin transducers between its two stator-rings. A flexural mode traveling wave is excited in each stator-ring, and two rotors assembled on a shaft are pressed on the driving surfaces of the stator-rings and propelled by the friction force between the stator-rings and rotors. Assisted by the finite element method (FEM), the size of the stator is determined. Operating principle is confirmed by the results of vibration measurement and FEM. Major mechanical and thermal characteristics of the prototype ultrasonic motor have been measured and discussed. 2. Structure and materials As shown in Fig. 1, the dual stator-ring rotary ultrasonic motor is composed of a base, dual rotor, shaft, frame, stator and nut. Rotors A and B have the same structure. The stator is fastened on the frame, rotors A and B are pressed on the tooth plates of stator through the shaft. The nut is screwed to the end of the shaft and used to press
X. Lu et al. / Sensors and Actuators A 189 (2013) 504–511
505
Table 1 Material constants (T0 = 20 ◦ C). Material
PZT-8H
Density (kg/m3 )
7650 ⎛ 12.06
Elastic modulus (×109 N/m2 )
⎜ ⎜ ⎝
Poisson’s ratio
0.31
Piezoelectric constant (C/m2 )
Mechanical quality factor, Qm Eletromechanical coupling factor, k33 Curie temperature, Tc (◦ C)
⎛
0 0 ⎜ 0 ⎜ ⎝ 0 12.7 0 800 0.6 300
Phosphor bronze 5.35 12.06
0 0 0 12.7 0 0
rotors A and B. Thus, the preload between the rotor and stator can also be adjusted by changing the nut location. The base fixed to the frame is used for protecting the rotor and stator and keep the axial location of the shaft. The dual rotor design is for enlarging the output power. Besides that, a piece of friction layer made of PTFE material, is bonded to the rotor’s two driving surfaces for obtaining a larger output power and making the motor performance more stable. Details about the stator are shown in Fig. 2. It mainly consists of two identical stator-rings with uniformly distributed teeth, and four Langevin transducers (1A, 1B, 2A and 2B) with identical structural size and material properties. The two stator-rings are connected by four driving bars, which are uniformly distributed along the circumference of motor, as shown in Fig. 2(a). Each driving bar is assembled at the center of corresponding Langevin transducer, as shown in Fig. 2(b) and (c). As shown in Fig. 2(c), each Langevin transducer is composed of one fastening screw, one front cover, two fixed plates, four bending piezoelectric plates, four electrodes, one driving bar and one bottom cover; each bending piezoelectric plate has two conversely polarized areas and the bending piezoelectric plates are stacked symmetrically about the driving bar and clamped by the fastening screw together. Transducers 1A and 1B are opposite spatially, and so are transducers 2A and 2B; the angular separation between transducers 1A and 2A is 90◦ , and so is that between transducers 1B and 2B. The size of the piezoelectric plate is 10 mm × 10 mm × 1 mm. The piezoelectric plates in transducer 1A have opposite polarization directions to their counterparts in transducer 1B. Thus when applied with the same driving voltage, transducers 1A and 1B have opposite bending directions,
5.15 5.15 10.45
0 0 0 3.13
0 0 0 0 3.13
8800
⎞
0 0 ⎟ 0 ⎟ 0 ⎠ 0 3.46
117
0.3
⎞
−5.2 −5.2 ⎟ 15.1 ⎟ 0 ⎠ 0 0
and so are the transducers 2A and 2B. This arrangement allows the effective excitation of the flexural mode in the stator-rings. Phosphor bronze is chosen for making the stator and metal parts of the transducers. Piezoelectric material used in the transducers is PZT-8H. Aluminum is used for making the rotor’s base. The relevant material properties are listed in Table 1. 3. Operation principle In the prototype motor, the ninth flexural vibration mode in the two stator-rings is employed, which has nine wavelengths along each stator-ring. Applied with an electrical voltage which has frequency close to the natural frequency of the ninth flexural mode, transducers 1A and 1B will vibrate in bending modes with phase difference of 180◦ , and their driving bars can excite a standing wave of the ninth flexural mode in each stator-ring, as shown in Fig. 3(a). When transducers 2A and 2B are applied with an electrical voltage with the same frequency and amplitude, another standing wave of the ninth flexural mode is excited in each stator-ring. Because the angular separation between two adjacent transducers in the motor is 90◦ , the two standing waves in each stator-ring have spatial phase difference of 1/4 wavelengths. When the two AC voltages applied to the transducers are out of phase by 90◦ in time, the resultant of these two standing waves in each stator-ring is a flexural vibration traveling wave along the circumference of the stator-ring, as shown in Fig. 3(b). Due to the symmetry of the vibration excitation structure described in Section 2, the two traveling waves in the stator-rings have the same propagation direction, which can be used to drive the rotors. 4. FEM based design and analyses From the operation principle of this motor, it is known that natural frequency of the first order bending mode of the Langevin transducers must be designed equal to natural frequency of the ninth order flexural mode of the stator-rings, in order that the stator can be efficiently excited. Based on this design point, a set of stator dimensions are determined by FEM calculation and size adjustment, as listed in Table 2. The properties of materials used in ANSYS calculation are listed in Table 1. Solid 226 (element type) Table 2 Size of the stator (unit: mm).
Fig. 1. Construction of the dual stator-ring rotary ultrasonic motor.
Parameter Value
D1 60
D2 40
W1 20
W2 4.5
W3 10
L1 20.4
T1 10
506
X. Lu et al. / Sensors and Actuators A 189 (2013) 504–511
(a)
D1
D2
Driving surface 2B
1B
2A
W2 1A
W1
Stator ring
W2
(b)
Moving direction
L1 Bending direction W3
T1
8
5
(c)
7
6 3 2 1 4 1.fastening screw; 2. front cover; 3&7. fixed plates; 4. bending piezoelectric components; 5. electrodes ; 6. driving bar; 8. bottom cover Fig. 2. Configuration of the stator. (a) The whole stator, (b) Langevin transducer, and (c) components and assembling of the Langevin transducer.
is chosen for the piezoelectric plates and solid 187 for the other parts. The number of tooth in each stator ring is 72, which is chosen according to our experiences [5]. Calculated natural frequencies of the stator-rings and transducers are around 42.3 kHz. Using the size listed in Table 2, the vibration of the whole stator is analyzed by FEM at 42.3 kHz, and the result is shown in Fig. 4. It confirms the vibration excitation principle of the standing wave in the stator-rings, shown in Fig. 3(a). The motional trajectory of a point (x = −25.45 mm, y = −11.05 mm, z = 14.50 mm) on the driving surface of stator is also simulated by the transient analysis module in ANSYS, for the operation in which transducers 1A and 1B are driven by a sinusoidal AC voltage with 42.3 kHz frequency and 100 V0-p
amplitude, and transducers 2A and 2B simultaneously by a cosine AC voltage with the same frequency and amplitude. In the calculation, each vibration period is divided into 10 steps, the calculating time contains 20 vibration periods, and the damping coefficient (=0.003) deduced from the measured vibration displacement of the stator is used. Calculated trajectory in the last vibration period of the point is plotted in Fig. 5. In the figure, the ellipse with thicker line is the trajectory of the point, and the other ellipses are its projections on the xy, xz and yz planes. This result indicates that the point has axial, tangential and radial vibration displacement, and its elliptical trajectory is not perpendicular to the driving surface (the xy plane).
X. Lu et al. / Sensors and Actuators A 189 (2013) 504–511
507
(a)
2A
1A
(b)
2B
1B
Traveling wave
Driving surface Fig. 3. Working principle. (a) Standing wave excited by transducers 1A and 1B and (b) traveling wave along the circumference of stator-ring.
5. Experimental results and discussion Based on the above design, a prototype motor is fabricated and assembled, and Fig. 6 is its image. Its appearance size is
Fig. 4. Calculated vibration pattern of the stator by FEM.
Fig. 5. Calculated motional trajectory of a point on driving surface.
80 mm × 80 mm × 53 mm. The rotor diameter is 58 mm and the friction material width is 2.5 mm. To effectively excite the traveling waves in the stator-rings, it is essential to make resonance frequencies of the first bending mode of the four transducers as close as possible. Owing to deviations of the component dimensions and assembling process parameters, the resonance frequencies are not exactly identical even if an identical tightening torque is used for their assembling. In the prototype fabrication, the resonance frequencies of the four transducers are tuned to be approximately identical by replacing the metal and piezoelectric components and changing the tightening torque. The frequency characteristics of impedance of the four transducers assembled in the motor are measured by precision impedance analyzer Agilent 4294A (with driving voltage 0.5 V0-p ), and the result is shown in Fig. 7. It is known that resonance frequencies of transducers 1A, 1B, 2A and 2B at 0.5 V0-p operating voltage are 39650 Hz, 39625 Hz, 39725 Hz and 39575 Hz, respectively, and the deviation among them is less than 0.25%. In Fig. 7, there are two resonance points for each transducer. Based on the following vibration measurement, it is known that the resonance point with higher frequency has the vibration pattern we need. Vibration characteristics of the stator are measured by a laser Doppler vibrometer system (PSV-300F-B). Fig. 8 shows the measured average vibration magnitude of one stator driving surface versus driving frequency when transducers 1A and 1B are driven by a 100 V0-p operating voltage, and the other transducers are short circuited. It is seen that the stator is in resonance at 38.97 kHz. This resonance frequency is less than the resonance frequencies of transducers 1A and 1B at 0.5 V0-p operating voltage because its driving voltage (100 V0-p ) is higher. When transducers 2A and 2B
Fig. 6. Image of the dual stator-ring rotary ultrasonic motor.
X. Lu et al. / Sensors and Actuators A 189 (2013) 504–511
(a)
-16 -32 -48 -64
Phase angle (°)
508
-80 1A
2A
1B Transducer
Fig. 8. Vibration magnitude of a driving surface versus operating frequency when transducers 1A and 1B are excited.
2B 38000
39000 40000 Frequency (Hz)
41000
42000
(b)
2220 1850 1480 1110
Impedance (Ω)
37000
740 1A
2A
1B Transducer
2B 37000
38000
39000
40000
41000
42000
Frequency (Hz) Fig. 7. Electrical characteristics of the transducers. (a) Phase angle versus frequency and (b) impedance versus frequency.
are driven by a 100 V0-p operating voltage, and the other transducers are short circuited, the measured resonance frequency of transducers 2A and 2B is 38.93 kHz, which is slightly different from the resonance frequency for transducers 1A and 1B (38.97 kHz). In the following experiments, unless otherwise specified, 38.97 kHz is used as the operating frequency, and 100 V0-p is used as the operating voltage; the preload between the rotor and stator is about 200 N. Fig. 9 shows the method to measure the out-of-plane vibration mode of the end surfaces of transducers 1A and 1B, and the measured result. It is seen that two end surfaces of transducers 1A and 1B vibrate out of phase by , which indicates that when one of the transducers bends upwards, another bends downwards. This result confirms the transducer vibration mode in the operation principle analysis and FEM result. Fig. 10 shows the method to measure the out-of-plane vibration mode of one of the driving surfaces when transducers 1A and 1B are driven and the other two are short circuited, and the measured result. A standing wave with 9 wavelengths can be clearly seen, which confirms the vibration mode of the driving surface in the principle analysis and FEM result.
Fig. 9. The out-of-plane vibration mode of the end surfaces of transducers 1A and 1B. (a) Measurement method and (b) result.
Fig. 10. The out-of-plane vibration mode of one of the driving surfaces when transducers 1A and 1B are excited. (a) Measurement method and (b) result.
X. Lu et al. / Sensors and Actuators A 189 (2013) 504–511
6
509
(a)
120
120
4 80 3 60
Power (W)
Speed (r/min)
100
2
40
Driving voltage: 250 V0-p
No-load speed (r/min)
5
110
100
90
Driving voltage: 250 V 0-p
1
20
80 0 0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0 1.8
-40
Torque (Nm) Fig. 11. Torque–speed characteristic of the prototype motor at the room temperature.
-20
0
20
40
60
80
100
Temperature (ºC)
(b)
Stalling torque (Nm)
1.6
1.4
1.2
Driving voltage : 250 V 0-p 1.0
-40
-20
0
20
40
60
80
100
Fig. 12. Experimental setup for measuring the response time of the prototype motor.
The standing wave has amplitude of 1.5 m when the operating frequency and voltage are 38.97 kHz and 100 V0-p , respectively. The speed–torque curve is measured at operating frequency of 38.97 kHz and operating voltage of 250 V0-p , at room temperature, and the measured result is shown in Fig. 11. It can be seen that the no-load speed is 120 r/min and the stalling torque is 1.6 Nm, and the maximum output power is about 5.5 W and the corresponding
Maximum output power (W)
(c)
8
22.5
7
20
6
17
5 15 4 Driving voltage: 250 V0-p
3
12
Maximum output power Maximum efficiency
2
10
1 -40
-20
0
20
40
60
Maximum efficiency (%)
Temperature (ºC)
80
100
7.5 120
Temperature (ºC) Fig. 14. Effects of ambient temperature on the performance of the prototype motor. (a) No-load speed, (b) stalling torque and (c) output power and the maximum efficiency.
Fig. 13. Recorded operating voltage and encoder signal for a starting state.
output torque is 0.9 Nm. According to the measurement, the maximum efficiency of 20.8% occurs at load torque of 0.8 Nm. In order to investigate the response time of the prototype motor, a measurement system shown in Fig. 12, is built. In the system, a frequency tunable motor controller is used to provide sinusoidal and cosine operating voltages to the motor. A rotary encoder is fixed to the shaft of the prototype motor for measuring the rotor’s speed. Oscilloscope DPO2014 is used to monitor the change of the sinusoidal wave voltage from the motor controller and the square wave
510
X. Lu et al. / Sensors and Actuators A 189 (2013) 504–511
to the square of its vibration velocity. Based on these conclusions and Fig. 15, it is known that the vibration velocity of the prototype motor is approximately proportional to the root of operating voltage in the operating voltage range and the maximum output power state, which may be caused by non-linearity of the motor system. Compared with the traditional traveling-wave rotary ultrasonic motors with the same stator outer diameter [5], our prototype motor has the following merits. Due to the use of dual stator-ring structure, our prototype has an increase of about 60% of output torque; due to the use of Langevin transducers rather than bonded piezoelectric rings, it can stand relatively high ambient temperature without the fall-off of piezoelectric ring, which often occurs in the temperature test of ultrasonic motors with bonded piezoelectric rings; due to the use of Langevin transducers between the two stator-rings, our prototype has a compact structure. 6. Summary Fig. 15. Measured temperatures after 3 min operation. P1 is for the driving surface and P2 for the piezoelectric plates.
signal from the rotary encoder. Once the motor controller works, the motor receives the operating voltages and starts to rotate. And then, the rotary encoder outputs signal. The signal wave is captured and recorded by DPO2014. The time delay from the first sine wave to the first square wave is defined as the run-up response time. Fig. 13 shows the recorded result, in which wave No. 1 represents the signal from the encoder, and wave No. 2 the operating voltage. The measured run-up response time is 3.6 ms, which indicates the response time of this motor is similar to the traditional traveling wave rotary ultrasonic motor with the same stator outer diameter (∼3.0 ms). Fig. 14 shows the measured dependency of the no-load speed, stalling torque, maximum output power and efficiency (for mechanical load) on ambient temperature. This measurement is carried out by a temperature control chamber (CH250C) system, the operating voltage is 250 V0-p and the motor works at resonance. They have peak values at 20 ◦ C ambient temperature, which means for the applied tightening torque, this motor has the best mechanical characteristics at 20 ◦ C ambient temperature. This is because the preload used in our prototype motor is optimal only for 20 ◦ C ambient temperature, and as the ambient temperature deviates from 20 ◦ C, the difference between this fixed preload and optimal one increases. As the ambient temperature increases or decreases, the driving performance becomes lower. At high ambient temperature of 100 ◦ C, the no-load speed and stalling torque decrease about 40%, and the decrease of the maximum output power is more than 50%. Even so, there are still 80 r/min no-load speed and 0.9 Nm stalling torque at 100 ◦ C, which is not inferior to the traditional traveling wave rotary ultrasonic motors [5]. The temperature of the driving surface and piezoelectric plates after 3 min operation were measured at different driving voltages when the motor operates at maximum output power and room temperature (20 ◦ C). Measuring point P1 for the driving surface is on the outer circle of the driving surface and circumferentially at the driving bar of transducer 2A, and measuring point P2 for the piezoelectric plates is in the middle of the side surfaces of piezoelectric plates in transducer 2A. According to our observation, measuring points P1 and P2 have the maximum temperature along the outer circle of the driving surface and on the side surfaces of the piezoelectric plates, respectively. The measured result is shown in Fig. 15. It shows that the temperatures after 3 min operation increase linearly with the driving voltage. Our previous research on temperature fields of piezoelectric devices [19,20] shows that temperature rise of a piezoelectric device is proportional to power dissipation of the device, and the power dissipation is proportional
A dual stator-ring rotary ultrasonic motor, which uses four first bending mode Langevin transducers evenly distributed between its two stator rings to excite the traveling waves in its stator-rings, has been proposed and investigated. FEM is used to design the dimensions of the motor to make the stator-rings and Langevin transducers operate in resonance. Experimental measurement and FEM analysis are used to confirm the operating principle. The prototype motor has the overall size of 80 mm × 80 mm × 53 mm, the stator outer diameter of 60 mm, and the operating frequency around 39 kHz. At the room temperature and 250 V0-p operating voltage, its stalling torque is 1.6 Nm, no-load speed is 120 rpm, and maximum output power of 5.5 W. The temperature characteristics of the no-load speed, installing torque and maximum torque are experimentally clarified, as well as the operating voltage dependency of the temperature at the driving interface and piezoelectric elements for the maximum output power state. Our experiments show that this motor has a larger output torque than the traditional traveling wave rotary ultrasonic motor with the same stator outer diameter; it can stand relatively high ambient temperature without the fall-off of piezoelectric rings. Acknowledgements This work is supported by the following funding organizations in China: Nanjing University of Aeronautics and Astronautics (Nos. NZ2010002 and S0896-013), Innovation and Entrepreneurship Program of Jiangsu, National Science Foundation of China (Nos. 51205203, 51275228, 51075212 and 91123020), the “111” Project (B12021) and PAPD. References [1] T. Sashida, Motor device utilizing ultrasonic oscillation, US Patent No. 4562374, 1985. [2] J. Wallaschek, Piezoelectric ultrasonic motors, Journal of Intelligent Material Systems and Structures 6 (1995) 71–83. [3] S. Ueha, Y. Tomikawa, Ultrasonic Motors Theory and Applications, Oxford Science Publications, New York, 1993. [4] K. Uchino, Piezoelectric Actuator and Ultrasonic Motors, Kluwer Academic Publishers, Boston, MA, 1997. [5] C.S. Zhao, Ultrasonic Motors Technologies and Applications, vol. 192–193, Science Press, Beijing, 2010, 432. [6] S.X. Dong, S.P. Lim, K.H. Lee, J.D. Zhang, L.C. Lim, K. Uchino, Piezoelectric ultrasonic micromotor with 1.5 mm diameter, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 50 (2003) 361–367. [7] C.H. Yun, L.Y. Yeo, J.R. Friend, B. Yan, Multi-degree-of-freedom ultrasonic micromotor for guidewire and catheter navigation: the neuroguide actuator, Applied Physics Letters 100 (2012) 164101. [8] J.M. Jin, D.D. Wan, Y. Yang, Q. Li, M. Zha, A linear ultrasonic motor using (K0.5 Na0.5 )NbO3 based lead-free piezoelectric ceramics, Sensors and Actuators A: Physical 165 (2011) 410–414.
X. Lu et al. / Sensors and Actuators A 189 (2013) 504–511 [9] Y. Yin, S. Zhou, C. Chen, C. Zhao, J. Jin, Operating mechanism of dual traveling wave of rotary ultrasonic motor, Proceedings of the Chinese Society of Electrical Engineering 31 (33) (2011) 101–108. [10] G. Wang, Z. Zhao, J. Guo, A high torque ultrasonic motor structured by double-stators and double-rotors, China Mechanical Engineering 23 (9) (2012) 1036–1041. [11] T. Morita, T. Niino, H. Asama, Rotational feedthrough using ultrasonic motor for high vacuum condition, Vacuum 65 (2002) 85–90. [12] M.K. Kurosawa, O. Kodaira, Y. Tsuchitoi, T. Higuchi, Transducer for high speed and large thrust ultrasonic linear motor using two sandwich-type vibrators, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 45 (1998) 1188–1195. [13] J. Satonobu, J.R. Friend, K. Nakamura, S. Ueha, Numerical analysis of the symmetric hybrid transducer ultrasonic motor, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 48 (2001) 1625–1631. [14] A. Iula, M. Pappalardo, A high-power traveling wave ultrasonic motor, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 53 (2006) 1344–1351. [15] Y.X. Liu, W.S. Chen, P. Feng, J.K. Liu, A square-type rotary ultrasonic motor with four driving feet, Sensors and Actuators A: Physical 180 (2012) 113–119. [16] L. Petit, P. Gonnard, A multilayer TWILA ultrasonic motor, Sensors and Actuators A 149 (2009) 113–119. [17] S.W. Or, H.L.W. Chan, V.C. Lo, C.W. Yuen, Dynamics of an ultrasonic transducer used for wire bonding, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 45 (1998) 1453–1460. [18] X.J. Xian, S.Y. Lin, Study on the compound multi-frequency ultrasonic transducer in flexural vibration, Ultrasonics 48 (2008) 202–208. [19] J.H. Hu, Analyses of the temperature field in a bar-shaped piezoelectric transformer operating in longitudinal vibration mode, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 50 (2003) 594–600. [20] X.L. Lu, J.H. Hu, C.S. Zhao, Analyses of the temperature field of traveling wave rotary ultrasonic motor, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 58 (2011) 2708–2719.
511
Biographies Xiaolong Lu, born in 1984, is currently a Ph.D. candidate in State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, China. He received his master degree from Southeast University, China, in 2009. His research interests include design and experiments of ultrasonic motors driven in extreme environments. Junhui Hu received his Ph.D. degree from Tokyo Institute of Technology, Tokyo, Japan, in 1997, and B.E. and M.E. degrees in electrical engineering from Zhejiang University, Hangzhou, China, in 1986 and 1989, respectively. He is a Chang-Jiang Distinguished Professor of the Ministry of Education of China, director of Precision Driving Lab at Nanjing University of Aeronautics and Astronautics (NUAA), and deputy director of State Key Laboratory of Mechanics and Control of Mechanical Structures, China. He was a research engineer at the R&D Center of NEC-Tokin, Sendai, Japan, from November 1997 to February 1999; research fellow and postdoctoral fellow at Hong Kong Polytechnic University, Hong Kong, China, from 1999 to 2001; assistant professor at Nanyang Technological University, Singapore, from 2001 to 2005; and associate professor at the School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, from 2005 to 2010. His present research interest includes ultrasonic manipulators and actuators, piezoelectric transducers and transformers, physical effects of ultrasound, wireless drive of piezoelectric components, energy harvesting from oscillation, and other novel utilization of vibration. He won the Paper Prize from the Institute of Electronics, Information and Communication Engineers (Japan) as a first author in 1998, and was awarded the title of valued reviewer of Sensors and Actuators A: Physical and Ultrasonics. He has given six invited talks in international conferences, and is the honorary chairman of IWPMA 2011, held in USA. He is the author and co-author of more than 170 papers (including more than 50 full papers published in SCI international journals) and disclosed patents, and a senior member of IEEE.
Contents lists available at SciVerse ScienceDirect
Sensors and Actuators A: Physical journal homepage: www.elsevier.com/locate/sna
A novel dual stator-ring rotary ultrasonic motor Xiaolong Lu, Junhui Hu ∗ , Lin Yang, Chunsheng Zhao State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics & Astronautics, Nanjing 210016, China
a r t i c l e
i n f o
Article history: Received 4 September 2012 Received in revised form 6 November 2012 Accepted 6 November 2012 Available online 16 November 2012 Keywords: Rotary ultrasonic motor Flexural mode traveling wave Dual stator-ring Bending mode Langevin transducers
a b s t r a c t In this work, a novel dual stator-ring rotary ultrasonic motor is proposed, designed, fabricated and characterized for raising driving torque of the rotary ultrasonic motor operating in the flexural vibration mode. It uses four bending mode Langevin transducers, which are evenly distributed between its two identical stator rings, to excite the ninth order flexural mode traveling waves in the two stator-rings and drive its two rotors. Driving bars assembled at the center of the Langevin transducers are employed to excite two ninth order flexural standing waves spatially and temporally orthogonal to each other in each stator-ring, and form the traveling wave. Results of vibration measurement are used to confirm the operating principle, and the finite element method is used to design the motor size in order that the motor can operate in resonance. The appearance size of the motor is 80 mm × 80 mm × 53 mm, stator outer diameter is 60 mm, and operating frequency is around 39 kHz. The major mechanical and thermal characteristics of the motor have been measured. At the room temperature and 250 V0-p operating voltage, its stalling torque is 1.6 Nm, no-load speed is 120 rpm, and output power reaches the maximum (=5.5 W) with a driving torque of 0.9 Nm and speed of 54 rpm. At ambient temperature of 100 ◦ C, the motor still has stalling torque of 0.9 Nm and no-load speed of 79 rpm for a operating voltage of 250 V0-p , which means that this motor can operate in relatively high temperature environment. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Ultrasonic motors have the merits of high torque to volume ratio, high positioning precision, intrinsic holding torque, compared to the conventional electromagnetic motors [1–4]. Recent applications of ultrasonic motors include space explorations, ultraprecision measurement, biomedical equipment, etc. [5–7]. In these applications, high adaptability to environment and high reliability of ultrasonic motors are desired. Some ultrasonic motors with bonded piezoelectric components have good performances [3,4,8–10], but the piezoelectric wafer may fall off from the bonding layer after a long time operation or during the operation in high temperature environment [5]. Comparatively, ultrasonic motors excited by Langevin transducers are more reliable and competitive in environment adaptability and working life [11,14]. There have been a lot of reports on the ultrasonic motors excited by Langevin transducers, many of which use longitudinal or bending vibration mode or both of them for vibration excitation. Kurosawa et al. [12] proposed an ultrasonic linear motor using two sandwich-type vibrators for large thrust applications. Satonobu et al. [13] proposed an ultrasonic motor with symmetric hybrid transducers. Iula and Pappalardo [14] proposed a
∗ Corresponding author. E-mail addresses: [email protected], [email protected] (J. Hu). 0924-4247/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.sna.2012.11.009
high-power traveling wave ultrasonic motor with several transducers. Liu et al. [15] proposed a square-type rotary ultrasonic motor with four driving feet. More research efforts in this area could be found in Refs. [16–18]. These motors can output large power but their dimensions are usually big. Research of ultrasonic motors with compact structure and excited by Langevin transducers is significant for practical applications. In this work, we have proposed and developed a novel dual stator-ring rotary ultrasonic motor, which is excited by four evenly distributed Langevin transducers between its two stator-rings. A flexural mode traveling wave is excited in each stator-ring, and two rotors assembled on a shaft are pressed on the driving surfaces of the stator-rings and propelled by the friction force between the stator-rings and rotors. Assisted by the finite element method (FEM), the size of the stator is determined. Operating principle is confirmed by the results of vibration measurement and FEM. Major mechanical and thermal characteristics of the prototype ultrasonic motor have been measured and discussed. 2. Structure and materials As shown in Fig. 1, the dual stator-ring rotary ultrasonic motor is composed of a base, dual rotor, shaft, frame, stator and nut. Rotors A and B have the same structure. The stator is fastened on the frame, rotors A and B are pressed on the tooth plates of stator through the shaft. The nut is screwed to the end of the shaft and used to press
X. Lu et al. / Sensors and Actuators A 189 (2013) 504–511
505
Table 1 Material constants (T0 = 20 ◦ C). Material
PZT-8H
Density (kg/m3 )
7650 ⎛ 12.06
Elastic modulus (×109 N/m2 )
⎜ ⎜ ⎝
Poisson’s ratio
0.31
Piezoelectric constant (C/m2 )
Mechanical quality factor, Qm Eletromechanical coupling factor, k33 Curie temperature, Tc (◦ C)
⎛
0 0 ⎜ 0 ⎜ ⎝ 0 12.7 0 800 0.6 300
Phosphor bronze 5.35 12.06
0 0 0 12.7 0 0
rotors A and B. Thus, the preload between the rotor and stator can also be adjusted by changing the nut location. The base fixed to the frame is used for protecting the rotor and stator and keep the axial location of the shaft. The dual rotor design is for enlarging the output power. Besides that, a piece of friction layer made of PTFE material, is bonded to the rotor’s two driving surfaces for obtaining a larger output power and making the motor performance more stable. Details about the stator are shown in Fig. 2. It mainly consists of two identical stator-rings with uniformly distributed teeth, and four Langevin transducers (1A, 1B, 2A and 2B) with identical structural size and material properties. The two stator-rings are connected by four driving bars, which are uniformly distributed along the circumference of motor, as shown in Fig. 2(a). Each driving bar is assembled at the center of corresponding Langevin transducer, as shown in Fig. 2(b) and (c). As shown in Fig. 2(c), each Langevin transducer is composed of one fastening screw, one front cover, two fixed plates, four bending piezoelectric plates, four electrodes, one driving bar and one bottom cover; each bending piezoelectric plate has two conversely polarized areas and the bending piezoelectric plates are stacked symmetrically about the driving bar and clamped by the fastening screw together. Transducers 1A and 1B are opposite spatially, and so are transducers 2A and 2B; the angular separation between transducers 1A and 2A is 90◦ , and so is that between transducers 1B and 2B. The size of the piezoelectric plate is 10 mm × 10 mm × 1 mm. The piezoelectric plates in transducer 1A have opposite polarization directions to their counterparts in transducer 1B. Thus when applied with the same driving voltage, transducers 1A and 1B have opposite bending directions,
5.15 5.15 10.45
0 0 0 3.13
0 0 0 0 3.13
8800
⎞
0 0 ⎟ 0 ⎟ 0 ⎠ 0 3.46
117
0.3
⎞
−5.2 −5.2 ⎟ 15.1 ⎟ 0 ⎠ 0 0
and so are the transducers 2A and 2B. This arrangement allows the effective excitation of the flexural mode in the stator-rings. Phosphor bronze is chosen for making the stator and metal parts of the transducers. Piezoelectric material used in the transducers is PZT-8H. Aluminum is used for making the rotor’s base. The relevant material properties are listed in Table 1. 3. Operation principle In the prototype motor, the ninth flexural vibration mode in the two stator-rings is employed, which has nine wavelengths along each stator-ring. Applied with an electrical voltage which has frequency close to the natural frequency of the ninth flexural mode, transducers 1A and 1B will vibrate in bending modes with phase difference of 180◦ , and their driving bars can excite a standing wave of the ninth flexural mode in each stator-ring, as shown in Fig. 3(a). When transducers 2A and 2B are applied with an electrical voltage with the same frequency and amplitude, another standing wave of the ninth flexural mode is excited in each stator-ring. Because the angular separation between two adjacent transducers in the motor is 90◦ , the two standing waves in each stator-ring have spatial phase difference of 1/4 wavelengths. When the two AC voltages applied to the transducers are out of phase by 90◦ in time, the resultant of these two standing waves in each stator-ring is a flexural vibration traveling wave along the circumference of the stator-ring, as shown in Fig. 3(b). Due to the symmetry of the vibration excitation structure described in Section 2, the two traveling waves in the stator-rings have the same propagation direction, which can be used to drive the rotors. 4. FEM based design and analyses From the operation principle of this motor, it is known that natural frequency of the first order bending mode of the Langevin transducers must be designed equal to natural frequency of the ninth order flexural mode of the stator-rings, in order that the stator can be efficiently excited. Based on this design point, a set of stator dimensions are determined by FEM calculation and size adjustment, as listed in Table 2. The properties of materials used in ANSYS calculation are listed in Table 1. Solid 226 (element type) Table 2 Size of the stator (unit: mm).
Fig. 1. Construction of the dual stator-ring rotary ultrasonic motor.
Parameter Value
D1 60
D2 40
W1 20
W2 4.5
W3 10
L1 20.4
T1 10
506
X. Lu et al. / Sensors and Actuators A 189 (2013) 504–511
(a)
D1
D2
Driving surface 2B
1B
2A
W2 1A
W1
Stator ring
W2
(b)
Moving direction
L1 Bending direction W3
T1
8
5
(c)
7
6 3 2 1 4 1.fastening screw; 2. front cover; 3&7. fixed plates; 4. bending piezoelectric components; 5. electrodes ; 6. driving bar; 8. bottom cover Fig. 2. Configuration of the stator. (a) The whole stator, (b) Langevin transducer, and (c) components and assembling of the Langevin transducer.
is chosen for the piezoelectric plates and solid 187 for the other parts. The number of tooth in each stator ring is 72, which is chosen according to our experiences [5]. Calculated natural frequencies of the stator-rings and transducers are around 42.3 kHz. Using the size listed in Table 2, the vibration of the whole stator is analyzed by FEM at 42.3 kHz, and the result is shown in Fig. 4. It confirms the vibration excitation principle of the standing wave in the stator-rings, shown in Fig. 3(a). The motional trajectory of a point (x = −25.45 mm, y = −11.05 mm, z = 14.50 mm) on the driving surface of stator is also simulated by the transient analysis module in ANSYS, for the operation in which transducers 1A and 1B are driven by a sinusoidal AC voltage with 42.3 kHz frequency and 100 V0-p
amplitude, and transducers 2A and 2B simultaneously by a cosine AC voltage with the same frequency and amplitude. In the calculation, each vibration period is divided into 10 steps, the calculating time contains 20 vibration periods, and the damping coefficient (=0.003) deduced from the measured vibration displacement of the stator is used. Calculated trajectory in the last vibration period of the point is plotted in Fig. 5. In the figure, the ellipse with thicker line is the trajectory of the point, and the other ellipses are its projections on the xy, xz and yz planes. This result indicates that the point has axial, tangential and radial vibration displacement, and its elliptical trajectory is not perpendicular to the driving surface (the xy plane).
X. Lu et al. / Sensors and Actuators A 189 (2013) 504–511
507
(a)
2A
1A
(b)
2B
1B
Traveling wave
Driving surface Fig. 3. Working principle. (a) Standing wave excited by transducers 1A and 1B and (b) traveling wave along the circumference of stator-ring.
5. Experimental results and discussion Based on the above design, a prototype motor is fabricated and assembled, and Fig. 6 is its image. Its appearance size is
Fig. 4. Calculated vibration pattern of the stator by FEM.
Fig. 5. Calculated motional trajectory of a point on driving surface.
80 mm × 80 mm × 53 mm. The rotor diameter is 58 mm and the friction material width is 2.5 mm. To effectively excite the traveling waves in the stator-rings, it is essential to make resonance frequencies of the first bending mode of the four transducers as close as possible. Owing to deviations of the component dimensions and assembling process parameters, the resonance frequencies are not exactly identical even if an identical tightening torque is used for their assembling. In the prototype fabrication, the resonance frequencies of the four transducers are tuned to be approximately identical by replacing the metal and piezoelectric components and changing the tightening torque. The frequency characteristics of impedance of the four transducers assembled in the motor are measured by precision impedance analyzer Agilent 4294A (with driving voltage 0.5 V0-p ), and the result is shown in Fig. 7. It is known that resonance frequencies of transducers 1A, 1B, 2A and 2B at 0.5 V0-p operating voltage are 39650 Hz, 39625 Hz, 39725 Hz and 39575 Hz, respectively, and the deviation among them is less than 0.25%. In Fig. 7, there are two resonance points for each transducer. Based on the following vibration measurement, it is known that the resonance point with higher frequency has the vibration pattern we need. Vibration characteristics of the stator are measured by a laser Doppler vibrometer system (PSV-300F-B). Fig. 8 shows the measured average vibration magnitude of one stator driving surface versus driving frequency when transducers 1A and 1B are driven by a 100 V0-p operating voltage, and the other transducers are short circuited. It is seen that the stator is in resonance at 38.97 kHz. This resonance frequency is less than the resonance frequencies of transducers 1A and 1B at 0.5 V0-p operating voltage because its driving voltage (100 V0-p ) is higher. When transducers 2A and 2B
Fig. 6. Image of the dual stator-ring rotary ultrasonic motor.
X. Lu et al. / Sensors and Actuators A 189 (2013) 504–511
(a)
-16 -32 -48 -64
Phase angle (°)
508
-80 1A
2A
1B Transducer
Fig. 8. Vibration magnitude of a driving surface versus operating frequency when transducers 1A and 1B are excited.
2B 38000
39000 40000 Frequency (Hz)
41000
42000
(b)
2220 1850 1480 1110
Impedance (Ω)
37000
740 1A
2A
1B Transducer
2B 37000
38000
39000
40000
41000
42000
Frequency (Hz) Fig. 7. Electrical characteristics of the transducers. (a) Phase angle versus frequency and (b) impedance versus frequency.
are driven by a 100 V0-p operating voltage, and the other transducers are short circuited, the measured resonance frequency of transducers 2A and 2B is 38.93 kHz, which is slightly different from the resonance frequency for transducers 1A and 1B (38.97 kHz). In the following experiments, unless otherwise specified, 38.97 kHz is used as the operating frequency, and 100 V0-p is used as the operating voltage; the preload between the rotor and stator is about 200 N. Fig. 9 shows the method to measure the out-of-plane vibration mode of the end surfaces of transducers 1A and 1B, and the measured result. It is seen that two end surfaces of transducers 1A and 1B vibrate out of phase by , which indicates that when one of the transducers bends upwards, another bends downwards. This result confirms the transducer vibration mode in the operation principle analysis and FEM result. Fig. 10 shows the method to measure the out-of-plane vibration mode of one of the driving surfaces when transducers 1A and 1B are driven and the other two are short circuited, and the measured result. A standing wave with 9 wavelengths can be clearly seen, which confirms the vibration mode of the driving surface in the principle analysis and FEM result.
Fig. 9. The out-of-plane vibration mode of the end surfaces of transducers 1A and 1B. (a) Measurement method and (b) result.
Fig. 10. The out-of-plane vibration mode of one of the driving surfaces when transducers 1A and 1B are excited. (a) Measurement method and (b) result.
X. Lu et al. / Sensors and Actuators A 189 (2013) 504–511
6
509
(a)
120
120
4 80 3 60
Power (W)
Speed (r/min)
100
2
40
Driving voltage: 250 V0-p
No-load speed (r/min)
5
110
100
90
Driving voltage: 250 V 0-p
1
20
80 0 0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0 1.8
-40
Torque (Nm) Fig. 11. Torque–speed characteristic of the prototype motor at the room temperature.
-20
0
20
40
60
80
100
Temperature (ºC)
(b)
Stalling torque (Nm)
1.6
1.4
1.2
Driving voltage : 250 V 0-p 1.0
-40
-20
0
20
40
60
80
100
Fig. 12. Experimental setup for measuring the response time of the prototype motor.
The standing wave has amplitude of 1.5 m when the operating frequency and voltage are 38.97 kHz and 100 V0-p , respectively. The speed–torque curve is measured at operating frequency of 38.97 kHz and operating voltage of 250 V0-p , at room temperature, and the measured result is shown in Fig. 11. It can be seen that the no-load speed is 120 r/min and the stalling torque is 1.6 Nm, and the maximum output power is about 5.5 W and the corresponding
Maximum output power (W)
(c)
8
22.5
7
20
6
17
5 15 4 Driving voltage: 250 V0-p
3
12
Maximum output power Maximum efficiency
2
10
1 -40
-20
0
20
40
60
Maximum efficiency (%)
Temperature (ºC)
80
100
7.5 120
Temperature (ºC) Fig. 14. Effects of ambient temperature on the performance of the prototype motor. (a) No-load speed, (b) stalling torque and (c) output power and the maximum efficiency.
Fig. 13. Recorded operating voltage and encoder signal for a starting state.
output torque is 0.9 Nm. According to the measurement, the maximum efficiency of 20.8% occurs at load torque of 0.8 Nm. In order to investigate the response time of the prototype motor, a measurement system shown in Fig. 12, is built. In the system, a frequency tunable motor controller is used to provide sinusoidal and cosine operating voltages to the motor. A rotary encoder is fixed to the shaft of the prototype motor for measuring the rotor’s speed. Oscilloscope DPO2014 is used to monitor the change of the sinusoidal wave voltage from the motor controller and the square wave
510
X. Lu et al. / Sensors and Actuators A 189 (2013) 504–511
to the square of its vibration velocity. Based on these conclusions and Fig. 15, it is known that the vibration velocity of the prototype motor is approximately proportional to the root of operating voltage in the operating voltage range and the maximum output power state, which may be caused by non-linearity of the motor system. Compared with the traditional traveling-wave rotary ultrasonic motors with the same stator outer diameter [5], our prototype motor has the following merits. Due to the use of dual stator-ring structure, our prototype has an increase of about 60% of output torque; due to the use of Langevin transducers rather than bonded piezoelectric rings, it can stand relatively high ambient temperature without the fall-off of piezoelectric ring, which often occurs in the temperature test of ultrasonic motors with bonded piezoelectric rings; due to the use of Langevin transducers between the two stator-rings, our prototype has a compact structure. 6. Summary Fig. 15. Measured temperatures after 3 min operation. P1 is for the driving surface and P2 for the piezoelectric plates.
signal from the rotary encoder. Once the motor controller works, the motor receives the operating voltages and starts to rotate. And then, the rotary encoder outputs signal. The signal wave is captured and recorded by DPO2014. The time delay from the first sine wave to the first square wave is defined as the run-up response time. Fig. 13 shows the recorded result, in which wave No. 1 represents the signal from the encoder, and wave No. 2 the operating voltage. The measured run-up response time is 3.6 ms, which indicates the response time of this motor is similar to the traditional traveling wave rotary ultrasonic motor with the same stator outer diameter (∼3.0 ms). Fig. 14 shows the measured dependency of the no-load speed, stalling torque, maximum output power and efficiency (for mechanical load) on ambient temperature. This measurement is carried out by a temperature control chamber (CH250C) system, the operating voltage is 250 V0-p and the motor works at resonance. They have peak values at 20 ◦ C ambient temperature, which means for the applied tightening torque, this motor has the best mechanical characteristics at 20 ◦ C ambient temperature. This is because the preload used in our prototype motor is optimal only for 20 ◦ C ambient temperature, and as the ambient temperature deviates from 20 ◦ C, the difference between this fixed preload and optimal one increases. As the ambient temperature increases or decreases, the driving performance becomes lower. At high ambient temperature of 100 ◦ C, the no-load speed and stalling torque decrease about 40%, and the decrease of the maximum output power is more than 50%. Even so, there are still 80 r/min no-load speed and 0.9 Nm stalling torque at 100 ◦ C, which is not inferior to the traditional traveling wave rotary ultrasonic motors [5]. The temperature of the driving surface and piezoelectric plates after 3 min operation were measured at different driving voltages when the motor operates at maximum output power and room temperature (20 ◦ C). Measuring point P1 for the driving surface is on the outer circle of the driving surface and circumferentially at the driving bar of transducer 2A, and measuring point P2 for the piezoelectric plates is in the middle of the side surfaces of piezoelectric plates in transducer 2A. According to our observation, measuring points P1 and P2 have the maximum temperature along the outer circle of the driving surface and on the side surfaces of the piezoelectric plates, respectively. The measured result is shown in Fig. 15. It shows that the temperatures after 3 min operation increase linearly with the driving voltage. Our previous research on temperature fields of piezoelectric devices [19,20] shows that temperature rise of a piezoelectric device is proportional to power dissipation of the device, and the power dissipation is proportional
A dual stator-ring rotary ultrasonic motor, which uses four first bending mode Langevin transducers evenly distributed between its two stator rings to excite the traveling waves in its stator-rings, has been proposed and investigated. FEM is used to design the dimensions of the motor to make the stator-rings and Langevin transducers operate in resonance. Experimental measurement and FEM analysis are used to confirm the operating principle. The prototype motor has the overall size of 80 mm × 80 mm × 53 mm, the stator outer diameter of 60 mm, and the operating frequency around 39 kHz. At the room temperature and 250 V0-p operating voltage, its stalling torque is 1.6 Nm, no-load speed is 120 rpm, and maximum output power of 5.5 W. The temperature characteristics of the no-load speed, installing torque and maximum torque are experimentally clarified, as well as the operating voltage dependency of the temperature at the driving interface and piezoelectric elements for the maximum output power state. Our experiments show that this motor has a larger output torque than the traditional traveling wave rotary ultrasonic motor with the same stator outer diameter; it can stand relatively high ambient temperature without the fall-off of piezoelectric rings. Acknowledgements This work is supported by the following funding organizations in China: Nanjing University of Aeronautics and Astronautics (Nos. NZ2010002 and S0896-013), Innovation and Entrepreneurship Program of Jiangsu, National Science Foundation of China (Nos. 51205203, 51275228, 51075212 and 91123020), the “111” Project (B12021) and PAPD. References [1] T. Sashida, Motor device utilizing ultrasonic oscillation, US Patent No. 4562374, 1985. [2] J. Wallaschek, Piezoelectric ultrasonic motors, Journal of Intelligent Material Systems and Structures 6 (1995) 71–83. [3] S. Ueha, Y. Tomikawa, Ultrasonic Motors Theory and Applications, Oxford Science Publications, New York, 1993. [4] K. Uchino, Piezoelectric Actuator and Ultrasonic Motors, Kluwer Academic Publishers, Boston, MA, 1997. [5] C.S. Zhao, Ultrasonic Motors Technologies and Applications, vol. 192–193, Science Press, Beijing, 2010, 432. [6] S.X. Dong, S.P. Lim, K.H. Lee, J.D. Zhang, L.C. Lim, K. Uchino, Piezoelectric ultrasonic micromotor with 1.5 mm diameter, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 50 (2003) 361–367. [7] C.H. Yun, L.Y. Yeo, J.R. Friend, B. Yan, Multi-degree-of-freedom ultrasonic micromotor for guidewire and catheter navigation: the neuroguide actuator, Applied Physics Letters 100 (2012) 164101. [8] J.M. Jin, D.D. Wan, Y. Yang, Q. Li, M. Zha, A linear ultrasonic motor using (K0.5 Na0.5 )NbO3 based lead-free piezoelectric ceramics, Sensors and Actuators A: Physical 165 (2011) 410–414.
X. Lu et al. / Sensors and Actuators A 189 (2013) 504–511 [9] Y. Yin, S. Zhou, C. Chen, C. Zhao, J. Jin, Operating mechanism of dual traveling wave of rotary ultrasonic motor, Proceedings of the Chinese Society of Electrical Engineering 31 (33) (2011) 101–108. [10] G. Wang, Z. Zhao, J. Guo, A high torque ultrasonic motor structured by double-stators and double-rotors, China Mechanical Engineering 23 (9) (2012) 1036–1041. [11] T. Morita, T. Niino, H. Asama, Rotational feedthrough using ultrasonic motor for high vacuum condition, Vacuum 65 (2002) 85–90. [12] M.K. Kurosawa, O. Kodaira, Y. Tsuchitoi, T. Higuchi, Transducer for high speed and large thrust ultrasonic linear motor using two sandwich-type vibrators, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 45 (1998) 1188–1195. [13] J. Satonobu, J.R. Friend, K. Nakamura, S. Ueha, Numerical analysis of the symmetric hybrid transducer ultrasonic motor, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 48 (2001) 1625–1631. [14] A. Iula, M. Pappalardo, A high-power traveling wave ultrasonic motor, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 53 (2006) 1344–1351. [15] Y.X. Liu, W.S. Chen, P. Feng, J.K. Liu, A square-type rotary ultrasonic motor with four driving feet, Sensors and Actuators A: Physical 180 (2012) 113–119. [16] L. Petit, P. Gonnard, A multilayer TWILA ultrasonic motor, Sensors and Actuators A 149 (2009) 113–119. [17] S.W. Or, H.L.W. Chan, V.C. Lo, C.W. Yuen, Dynamics of an ultrasonic transducer used for wire bonding, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 45 (1998) 1453–1460. [18] X.J. Xian, S.Y. Lin, Study on the compound multi-frequency ultrasonic transducer in flexural vibration, Ultrasonics 48 (2008) 202–208. [19] J.H. Hu, Analyses of the temperature field in a bar-shaped piezoelectric transformer operating in longitudinal vibration mode, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 50 (2003) 594–600. [20] X.L. Lu, J.H. Hu, C.S. Zhao, Analyses of the temperature field of traveling wave rotary ultrasonic motor, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 58 (2011) 2708–2719.
511
Biographies Xiaolong Lu, born in 1984, is currently a Ph.D. candidate in State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, China. He received his master degree from Southeast University, China, in 2009. His research interests include design and experiments of ultrasonic motors driven in extreme environments. Junhui Hu received his Ph.D. degree from Tokyo Institute of Technology, Tokyo, Japan, in 1997, and B.E. and M.E. degrees in electrical engineering from Zhejiang University, Hangzhou, China, in 1986 and 1989, respectively. He is a Chang-Jiang Distinguished Professor of the Ministry of Education of China, director of Precision Driving Lab at Nanjing University of Aeronautics and Astronautics (NUAA), and deputy director of State Key Laboratory of Mechanics and Control of Mechanical Structures, China. He was a research engineer at the R&D Center of NEC-Tokin, Sendai, Japan, from November 1997 to February 1999; research fellow and postdoctoral fellow at Hong Kong Polytechnic University, Hong Kong, China, from 1999 to 2001; assistant professor at Nanyang Technological University, Singapore, from 2001 to 2005; and associate professor at the School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, from 2005 to 2010. His present research interest includes ultrasonic manipulators and actuators, piezoelectric transducers and transformers, physical effects of ultrasound, wireless drive of piezoelectric components, energy harvesting from oscillation, and other novel utilization of vibration. He won the Paper Prize from the Institute of Electronics, Information and Communication Engineers (Japan) as a first author in 1998, and was awarded the title of valued reviewer of Sensors and Actuators A: Physical and Ultrasonics. He has given six invited talks in international conferences, and is the honorary chairman of IWPMA 2011, held in USA. He is the author and co-author of more than 170 papers (including more than 50 full papers published in SCI international journals) and disclosed patents, and a senior member of IEEE.