Tham khảo tài liệu 'mechatronic systems, simulation, modeling and control part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 110 Mechatronic Systems Simulation Modelling and Control Fig. 7. Voltage current detecting unit. Fig. 8. Control unit with a microcomputer. time between rising edges of Pe and Tị the time between rising edge of Pe and trailing edge of Pi are measured by the unit as shown in Fig. 10. The phase difference is calculated from p-180 X . Tc 2 This value is measured as average in averaging factor Na cycles of pulse signal Pe. Thus the operating frequency is updated every Na cycles of the driving signals. The updated operating frequency fn 1 is given by f 1 - fn - Kp fa - 3 where fn is the operating frequency before update ộr is the admittance phase at resonance Ộ is the calculated admittance phase from eq. 2 at a frequency of fn Kp is a proportional feedback gain. To stabilize the tracing Kp should be selected as following inequality is satisfied. Resonance Frequency Tracing System for Langevin Type Ultrasonic Transducers 111 Fig. 9. Measurement of cycle and phase diference. K I 4 where S is the slope of the admittance phase vs. frequency curve at resonanse frequency. The updated frequency is transmitted to the DDS. Repeating this routine the operating frequency can approach resonance frequency of transducer. 4. Application for Ultrasonic Dental Scaler Ultrasonic dental scaler Ultrasonic dental scaler is an equipment to remove dental calculi from teeth. the scaler consists of a hand piece as shown in Fig. 10 and a driver circuit to excite vibration. A Langevin type ultrasonic transducer is mounted in the hand piece. the structure of the transducer is shown in Fig. 11. Piezoelectric elements are clamped by a tail block and a hone block. A tip is attached on the top of the horn. The blocks and the tip are made of stainless steel. The transducer vibrates longitudinally at first-order resonance frequency. One vibration node is located in the middle. To support the node the transducer is bound by a silicon rubber. To carry out the following experiments a sample scaler was
