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Optimum contact conditions for miniaturized surface acoustic wave linear motor
Ultrasonics 38 (2000) 51–53 www.elsevier.nl/locate/ultras
Optimum contact conditions for miniaturized surface acoustic wave linear motor Masaya Takasaki *, Minoru Kuribayashi Kurosawa 1, Toshiro Higuchi Department of Precision Engineering, Graduate School of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan
Abstract This paper reports the successful operation of a 70 MHz driving surface acoustic wave (SAW ) linear motor with a miniaturized stator transducer. This paper also deals with an investigation into an optimized slider design for the miniaturized SAW linear motor. The performance of three silicon type sliders, with different projection size, was compared. Output forces of the three sliders were measured with change of pre-load. It was found that the slider with smaller projection tended to produce greater output force. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Linear motor; Micro-actuator; Miniaturization; Surface acoustic wave; Ultrasonic motor
1. Introduction
2. Principle
The performance of a surface acoustic wave (SAW ) linear motor using a silicon slider driven at 10 MHz has already been reported [1,2]. Previously, a miniaturized SAW linear motor successfully worked at operating frequency of 50 MHz [3]. The output force of the 50 MHz motor was 36 mN, traverse speed was about 0.7 m/s. This performance is not even the best available, because there is a slider contact condition producing more output force and higher speed which has not been investigated yet. This paper reports an optimum contact condition which can accomplish higher performance. In this research, we focused on the design of a silicon slider. The silicon slider has a distribution of projections with radius 5–50 mm. The size of projection radius was evaluated as the slider contact conditions. The miniaturized SAW linear motor operated at 70 MHz was successfully driven. The operations of the miniaturized SAW linear motor will also be reported in this paper.
The SAW linear motor consists of a stator transducer and a slider. The stator transducer is a substrate of LiNbO 128° Y-cut X-Prop. An example of the stator 3 transducer is shown in Fig. 1. On the substrate surface, interdigital transducers are arranged to excite a Rayleigh wave, a kind of SAW. The Rayleigh wave propagates on the substrate surface. As the wave propagates, particles on the surface move along an elliptical locus as shown in Fig. 2. A slider arranged on the elastic substrate is driven by frictional force. The slider is preloaded so that adequate friction force can be provided. The slider is made of silicon. On the slider surface, projections are distributed so that sufficient contact pressure can be generated. The radius of the projection is 5–50 mm. Fig. 3 is a SEM photograph of the silicon slider surface.
* Corresponding author. Tel.: +81-3-5841-6466; fax: +81-3-5800-6968. E-mail address: [email protected] (M. Takasaki) 1 Present address: Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuda-cho, Midori-ku, Yokohama 226-8502, Japan.
3. Miniaturized motor Limits of the stator transducer dimensions such as the width and the thickness are proportional to the wavelength of the SAW. Therefore, by using higher operating frequency, a miniaturized transducer can be fabricated. Fig. 1 is a photograph of a miniaturized stator transducer operated at 70 MHz. The size of the transducer was 4.5×50×0.5 mm3.
0041-624X/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S0 0 4 1 -6 2 4 X ( 9 9 ) 0 0 09 3 - 1
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M. Takasaki et al. / Ultrasonics 38 (2000) 51–53
Fig. 4. The experimental setup for the miniaturized SAW linear motor.
Fig. 1. The miniaturized 4.5×50×0.5 mm3.
stator
transducer.
Dimensions
Fig. 5. The silicon slider on the magnet. Fig. 2. The principle of SAW motor driving.
the substrate and the iron plate could arrange the preload. The magnetic force was calibrated by gravity force acting on weights. The gravity was balanced with the magnetic force through a pulley and a wire. The transient responses of the 70 MHz SAW linear motor were measured at the pre-load of 160 mN. The responses are shown in Fig. 6. The output force calculated from acceleration and the slider weight was about
Fig. 3. A SEM photograph of the silicon slider surface.
Fig. 4 describes an experimental setup for a miniaturized SAW linear motor. The stator transducer was placed on an iron plate. The silicon slider was glued on a permanent magnet as shown in Fig. 5. The size of the silicon slider was 1.6×1.6×0.3 mm3. The dimension of the magnet was 2 mm in diameter and 1.8 mm high. The magnetic force provided the pre-load for the linear motor. The thickness of plastic plates sandwiched by
Fig. 6. Transient responses of the 70 MHz motor.
M. Takasaki et al. / Ultrasonics 38 (2000) 51–53
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5. Results For each slider, output forces with change in contact pressure were plotted in Fig. 7. Commonly, the characteristics peaked at certain pre-load pressure. The maximum output force of slider A was over 400 mN/mm2. In case of slider B, the maximum output force was about 500 mN/mm2. Slider C produced almost 700 mN/mm2. Generally, the silicon slider with smaller projections tended to achieve larger output force per slider contact area.
Fig. 7. Output forces versus pre-load pressure. Table 1 Size of the silicon sliders
Slider A Slider B Slider C
r (mm)
d (mm)
Number of projections
Total contact area (mm2)
46 23 4.8
997 500 111
4 20 226
0.026 0.0332 0.0164
23 mN. This was 14% of the pre-load. The traverse speed was 0.6 m/s.
4. Sliders To investigate the optimum slider projection size indicated by ‘r’ in Fig. 5, three types of silicon slider were prepared. Table 1 indicates the projection size of each silicon slider. The distance between projections was enough so long as the projection had no influence upon neighboring projections. Experiments were carried out at the operating frequency of 40 MHz and driving voltage of 48 V . For each slider, the output force with 0–p change in pre-load was measured. To evaluate performance equally, the output force was evaluated as the force per contact area (mm2), and the pre-load was described as contact pressure (MPa).
6. Conclusions A miniaturized SAW linear motor with operating frequency of 70 MHz could work successfully. The output force was 13 mN. The traverse speed was 0.6 m/s. The output force density against the silicon slider projection size was investigated using a 40 MHz motor. It was found that the slider with smaller projections produced larger output force per slider contact area. Nevertheless, it seems that slider C was not completely optimized in terms of size of projections. A silicon slider with much smaller projections is required to measure the output force. A detailed relationship between the projection size and the output force per contact area will ensue, and the maximum output force of this miniaturized SAW motor will be measured.
References [1] N. Osakabe, M. Kurosawa, T. Higuchi, O. Shinoura, Surface acoustic wave linear motor using silicon slider, Proc. IEEE Workshop on Micro Electro Mechanical Systems, Heidelberg, January 25–29 (1998) . [2] M.K. Kurosawa, N. Osakabe, K. Tojo, M. Takasaki, T. Higuchi, Surface acoustic wave linear motor with a silicon slider, Technical Report of IEICE, US98-33, 1998, pp. 55–62 (in Japanese). [3] M. Takasaki, N. Osakabe, M.K. Kurosawa, T. Higuchi, Miniaturization of surface acoustic wave linear motor, Proc. IEEE Ultrasonics Symp., Sendai, Japan (1998) 679–682.
Optimum contact conditions for miniaturized surface acoustic wave linear motor Masaya Takasaki *, Minoru Kuribayashi Kurosawa 1, Toshiro Higuchi Department of Precision Engineering, Graduate School of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan
Abstract This paper reports the successful operation of a 70 MHz driving surface acoustic wave (SAW ) linear motor with a miniaturized stator transducer. This paper also deals with an investigation into an optimized slider design for the miniaturized SAW linear motor. The performance of three silicon type sliders, with different projection size, was compared. Output forces of the three sliders were measured with change of pre-load. It was found that the slider with smaller projection tended to produce greater output force. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Linear motor; Micro-actuator; Miniaturization; Surface acoustic wave; Ultrasonic motor
1. Introduction
2. Principle
The performance of a surface acoustic wave (SAW ) linear motor using a silicon slider driven at 10 MHz has already been reported [1,2]. Previously, a miniaturized SAW linear motor successfully worked at operating frequency of 50 MHz [3]. The output force of the 50 MHz motor was 36 mN, traverse speed was about 0.7 m/s. This performance is not even the best available, because there is a slider contact condition producing more output force and higher speed which has not been investigated yet. This paper reports an optimum contact condition which can accomplish higher performance. In this research, we focused on the design of a silicon slider. The silicon slider has a distribution of projections with radius 5–50 mm. The size of projection radius was evaluated as the slider contact conditions. The miniaturized SAW linear motor operated at 70 MHz was successfully driven. The operations of the miniaturized SAW linear motor will also be reported in this paper.
The SAW linear motor consists of a stator transducer and a slider. The stator transducer is a substrate of LiNbO 128° Y-cut X-Prop. An example of the stator 3 transducer is shown in Fig. 1. On the substrate surface, interdigital transducers are arranged to excite a Rayleigh wave, a kind of SAW. The Rayleigh wave propagates on the substrate surface. As the wave propagates, particles on the surface move along an elliptical locus as shown in Fig. 2. A slider arranged on the elastic substrate is driven by frictional force. The slider is preloaded so that adequate friction force can be provided. The slider is made of silicon. On the slider surface, projections are distributed so that sufficient contact pressure can be generated. The radius of the projection is 5–50 mm. Fig. 3 is a SEM photograph of the silicon slider surface.
* Corresponding author. Tel.: +81-3-5841-6466; fax: +81-3-5800-6968. E-mail address: [email protected] (M. Takasaki) 1 Present address: Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuda-cho, Midori-ku, Yokohama 226-8502, Japan.
3. Miniaturized motor Limits of the stator transducer dimensions such as the width and the thickness are proportional to the wavelength of the SAW. Therefore, by using higher operating frequency, a miniaturized transducer can be fabricated. Fig. 1 is a photograph of a miniaturized stator transducer operated at 70 MHz. The size of the transducer was 4.5×50×0.5 mm3.
0041-624X/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S0 0 4 1 -6 2 4 X ( 9 9 ) 0 0 09 3 - 1
52
M. Takasaki et al. / Ultrasonics 38 (2000) 51–53
Fig. 4. The experimental setup for the miniaturized SAW linear motor.
Fig. 1. The miniaturized 4.5×50×0.5 mm3.
stator
transducer.
Dimensions
Fig. 5. The silicon slider on the magnet. Fig. 2. The principle of SAW motor driving.
the substrate and the iron plate could arrange the preload. The magnetic force was calibrated by gravity force acting on weights. The gravity was balanced with the magnetic force through a pulley and a wire. The transient responses of the 70 MHz SAW linear motor were measured at the pre-load of 160 mN. The responses are shown in Fig. 6. The output force calculated from acceleration and the slider weight was about
Fig. 3. A SEM photograph of the silicon slider surface.
Fig. 4 describes an experimental setup for a miniaturized SAW linear motor. The stator transducer was placed on an iron plate. The silicon slider was glued on a permanent magnet as shown in Fig. 5. The size of the silicon slider was 1.6×1.6×0.3 mm3. The dimension of the magnet was 2 mm in diameter and 1.8 mm high. The magnetic force provided the pre-load for the linear motor. The thickness of plastic plates sandwiched by
Fig. 6. Transient responses of the 70 MHz motor.
M. Takasaki et al. / Ultrasonics 38 (2000) 51–53
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5. Results For each slider, output forces with change in contact pressure were plotted in Fig. 7. Commonly, the characteristics peaked at certain pre-load pressure. The maximum output force of slider A was over 400 mN/mm2. In case of slider B, the maximum output force was about 500 mN/mm2. Slider C produced almost 700 mN/mm2. Generally, the silicon slider with smaller projections tended to achieve larger output force per slider contact area.
Fig. 7. Output forces versus pre-load pressure. Table 1 Size of the silicon sliders
Slider A Slider B Slider C
r (mm)
d (mm)
Number of projections
Total contact area (mm2)
46 23 4.8
997 500 111
4 20 226
0.026 0.0332 0.0164
23 mN. This was 14% of the pre-load. The traverse speed was 0.6 m/s.
4. Sliders To investigate the optimum slider projection size indicated by ‘r’ in Fig. 5, three types of silicon slider were prepared. Table 1 indicates the projection size of each silicon slider. The distance between projections was enough so long as the projection had no influence upon neighboring projections. Experiments were carried out at the operating frequency of 40 MHz and driving voltage of 48 V . For each slider, the output force with 0–p change in pre-load was measured. To evaluate performance equally, the output force was evaluated as the force per contact area (mm2), and the pre-load was described as contact pressure (MPa).
6. Conclusions A miniaturized SAW linear motor with operating frequency of 70 MHz could work successfully. The output force was 13 mN. The traverse speed was 0.6 m/s. The output force density against the silicon slider projection size was investigated using a 40 MHz motor. It was found that the slider with smaller projections produced larger output force per slider contact area. Nevertheless, it seems that slider C was not completely optimized in terms of size of projections. A silicon slider with much smaller projections is required to measure the output force. A detailed relationship between the projection size and the output force per contact area will ensue, and the maximum output force of this miniaturized SAW motor will be measured.
References [1] N. Osakabe, M. Kurosawa, T. Higuchi, O. Shinoura, Surface acoustic wave linear motor using silicon slider, Proc. IEEE Workshop on Micro Electro Mechanical Systems, Heidelberg, January 25–29 (1998) . [2] M.K. Kurosawa, N. Osakabe, K. Tojo, M. Takasaki, T. Higuchi, Surface acoustic wave linear motor with a silicon slider, Technical Report of IEICE, US98-33, 1998, pp. 55–62 (in Japanese). [3] M. Takasaki, N. Osakabe, M.K. Kurosawa, T. Higuchi, Miniaturization of surface acoustic wave linear motor, Proc. IEEE Ultrasonics Symp., Sendai, Japan (1998) 679–682.