Statistical analysis of resonance frequency error for ultrasonic welding machine transducer

Ultrasonic welding technology, a high efficiency and energy saving technology, has been widely used in industry. Piezoelectric transducer is the key component in ultrasonic welding machine, and the resonance frequency is the most important parameter of the piezotransducer. However, there are some fluctuations for the resonance frequencies of mass production piezotransducers because many factors influence, such as the microstructures of piezoelectric material and metal material changing, the size and the distribution of material grains being not uniform, machining error, assembling error, and stress being not uniform and so on. These fluctuations could cause it difficult for ultrasonic generator to matching, and influence on acoustic impedance and the output acoustic power. In this paper, the author carries out statistical analysis for the resonance frequencies and obtains the histogram of the resonance frequencies by data analysis method after testing the resonance frequencies of a group of mass production piezotransducers. According to the histogram the distribution curve of the resonance frequency can be fitted, and this curve shows the distribution of the resonance frequency is close to Normal distribution. Following, this paper discusses influence rules of the pressure and the surface roughness, and the constant-torque assembly method based on PC control is presented. Finally the author suggests the numerical control modifying method for piezotransducer and ultrasonic horn can be used. The paper has certain directive significance to the piezotransducer design, the mass production of ultrasonic welding machine and acoustic system matching.