Piezoelectric Sensors and Actuators

Development and the application of new piezoelectric sensors and actuators using micro-nano technology are done. For instance,
　　（1）Touch sensor for micromanipulation with high sensitivity and high rigidity,
　　（2）Tactile sensor for robot with high sensitivity and wide measurement range,
　　（3）Tailor-made multilayer piezoelectric actuator having large displacements and forces.
Additionally, since piezoelectric ceramics (PZT) contain lead, the research on lead-free piezoelectric ceramics ((K,Na)(Nb,Ta)O3 ceramics and CaBi4Ti4O15 thin film) is done.

Touch Sensor for Micromanipulation Using Lead-Free (K,Na)(Nb,Ta)O3 Ceramics

In the field of applied microbiology, a touch sensor for micromanipulation with a pipette is needed (Fig. 1). Therefore, we developed a touch sensor using Pb(Zr,Ti)O3 (PZT). The piezoelectric material is used for vibration of the pipette and for measurement of the change in mechanical impedance caused by the pipette tip contacting the object being measured. However, the lead included in PZT can cause environmental problems. Therefore, we developed a touch sensor using lead-free (K,Na)(Nb,Ta)O3 ceramics (KNNT ceramics) (Fig. 2), which are strong candidates for lead-free piezoelectric ceramics. In this study, characteristics of a touch sensor utilizing piezoelectric vibration were theoretically derived. The results show that the piezoelectric constant d31 is very important: the higher the mode of vibration, the smaller the tip amplitude; the lower the mode of vibration, the higher the sensitivity. Also, the higher the elasticity or viscosity of the object in contact with the sensor, the higher the sensitivity. These theoretical results qualitatively correspond to experimental results. The piezoelectric constant d31 of KNNT ceramics was measured for the first time, and its value was found to be greater than or equal to 100 pm/V. KNNT ceramics were applied to the touch sensor and its utility was confirmed (Fig. 3-4).

[1] K. Motoo, F. Arai, T. Fukuda, T. Katsuragi, and K. Itoigawa, High sensitive touch sensor with piezoelectric thin film for pipetting works under microscope, Sensors and Actuators A 126, pp. 1-6, 2006.

[2] K. Motoo, F. Arai, T. Fukuda, M. Matsubara, K. Kikuta, T. Yamaguchi, and S. Hirano, Touch sensor for micromanipulation with pipette using lead-free (K, Na)(Nb, Ta)O3 piezoelectric ceramics, J. Appl. Phys., Vol. 98, 094505, 2005.

Tactile Sensor for Robot with High Sensitivity and Wide Measurement Range

We propose a new tactile sensor utilizing piezoelectric vibration. This tactile sensor has a high sensitivity, wide measurement range, pressure resistance, flexibility, and self-sensing function. This tactile sensor comprises two piezoelectric materials. One is used for the vibration of the sensor element and the other is used for the measurement of the change in mechanical impedance induced by an external force. We achieved the wide measurement range by implementing two ideas. One was to apply the external force to the sensor element through an elastic body and the other was to use two or more modes of vibration. Moreover, for the elastic body, it is preferable to use a material whose elasticity and viscosity are easily changed by an external force, such as a gel. In this study, first, this tactile sensor was analyzed, and then its characteristics were derived. The analytical results qualitatively corresponded to the experimental results. Next, a prototype tactile sensor was fabricated and evaluated. The evaluation results showed that this tactile sensor can measure a pressure of 2.5 Pa or less and a pressure of 10 kPa or more (Fig. 1) and its pressure resistance is 1 MPa or more. Additionally, the integration of the piezoelectric vibration-type tactile sensor (Fig. 2) and the application to the object grasping (Fig. 3) were done.

[1] K. Motoo, F. Arai, and T. Fukuda, Piezoelectric Vibration-Type Tactile Sensor Using Elasticity and Viscosity Change of Structure, Journal of the Robotics Society of Japan, Vol. 24, No. 3, pp. 408-415 (2006) (in Japanese).

[2] K. Motoo, T. Fukuda, F. Arai, and T. Matsuno, Piezoelectric Vibration-Type Tactile Sensor with Wide Measurement Range Using Elasticity and Viscosity Change, Proceedings of the 2006 IEEE/RSJ International Conference on Intelligent Robots and Systems, pp. 1946-1951, 2006.

Tailor-Made Multilayer Piezoelectric Actuator Using Lead-Free (K,Na)(Nb,Ta)O3 Ceramics

We propose tailor-made multilayer piezoelectric actuators (TAMPA) having large displacements and large forces (Fig. 1). In existing piezoelectric actuators, production of small, low-cost actuators having large displacements and large forces is difficult to achieve. We solved this problem by combining two bimorph-type piezoelectric elements with both ends simply supported, and stacking several elements on top of each other. Moreover, TAMPA is a tailor-made actuator whose displacement to force ratio can be varied widely by adjusting the size of the bimorph-type piezoelectric elements even when the total size of the actuator is kept constant. In this study, the bimorph-type piezoelectric element was analyzed, and the relationship between the displacement and the force under fixed conditions was experimentally determined. The relationship between the displacement and the force of TAMPA was theoretically derived. The analytical results showed that a TAMPA having dimensions of approximately 10×10×10 mm is capable of generating displacements of several hundred μm or the force of several N. A prototype was produced and its performance was evaluated. These results agreed well with the analytical results, confirming the validity of the analytical results. Finally, because the lead in PZT can cause environmental problems, a TAMPA was produced that used (K,Na)(Nb,Ta)O3 piezoelectric ceramics instead of PZT.

Fig. 1 Structure of Tailor-made Multilayer Piezoelectric Actuator (TAMPA), the displacement to force ratio of which can be varied considerably by adjusting the size of the bimorph-type piezoelectric elements even if the overall size of the actuator is kept constant.

[1] K. Motoo, N. Toda, F. Arai, T. Fukuda, T. Matsuno, K. Kikuta, and S. Hirano, Tailor-made Multilayer Piezoelectric Actuator Having Large Displacements and Forces, Journal of the Japan Society of Mechanical Engineers (C), Vol. 72, No. 722, pp. 232-239 (2006) (in Japanese).

[2] K. Motoo, N. Toda, T. Fukuda, F. Arai, K. Kikuta, S. Hirano, and T. Matsuno, Tailor-made multilayer piezoelectric actuator having large displacements and forces produced from lead-free piezoelectric ceramics, IEEE International Symposium on Micro-NanoMechatronics and Human Science, pp. 137-142, 2006.

Research Projects 2005

Signal Processing of GPR acquired by Geography Adaptive Scanning
Fuzzy Sensor Fusion for Anti Personal Land Mine Detection
Landmine Surveying System with Low-ground-pressure Vehicle