Tham khảo tài liệu 'mechatronic systems, simulation, modeling and control 2012 part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 114 Mechatronic Systems Simulation Modelling and Control estimation can be applied. To discuss the possibility of the diagnosis the frequency shifts were measured using the experimental apparatus as shown in Fig. 15. A sample was supported by an aluminum disk through a silicon rubber sheet. The transducer was fed by a z-stage and contacted with the sample. The contact load was measured by load cells under the aluminum disk. This measuring configuration was used in the following experiments. The combination factor were observed in various materials. The natural frequency shifts in contact with various materials were measured with the change of contact load. The shape and size of the sample was rectangular solid and 20 mm x 20 mm x 5 mm except the LiNbOs sample. the size of the LiNbOs sample was 20 mm x 20 mm x 1 mm. The results are plotted in Fig. 16. the natural frequency of the transducer decreased with the increase of contact load in the case of soft material with high damping factor such as rubber. The natural frequency did not change so much in the case of silicon rubber. The natural frequency increased in the case of other materials. Comparing steel SS400 and aluminum stiffness of steel is higher than that of aluminum. Frequency shift of LiNbOs is larger than that of steel Fig. 15. Experimental apparatus for measurement of the frequency shifts with contact. B---LiNbO 3 e---Steel SS400 -A---Aluminium - ---Acrylic - ---Silicon rubber - ---Rubber Fig. 16. Measurement of natural frequency shifts with the change of contact load in contact with various materials. Resonance Frequency Tracing System for Langevin Type Ultrasonic Transducers 115 within 4 N though stiffness of LiNbOs is approximately same as that of steel. This means that mechanical Q factor of LiNbOs is higher than that of steel namely damping factor of LiNbOs is lower. Frequency shift of LiNbOs was saturated above 5 N. The reason can be considered that effect of the silicon rubber sheet appeared in the
