超声焊接全状态频率跟踪算法*

与超声塑料焊接相比，超声金属焊接负载重且变化剧烈，容易导致换能器出现无阻性点状态或者频率误跟踪。现有的频率跟踪方法往往只能在换能器有阻性点的状态下正常工作，在出现误跟踪时也无法自动复位。针对上述问题，本文基于梅森等效电路，推导出一种能够同时适配于谐振频率与反谐振频率，能够自行判断是否误跟踪频率跟踪算法。当换能器处于无阻性点状态时，算法将自动把跟踪目标变为相位差最小点，实现全状态频率跟踪。算法利用三个不同频率及其发波时换能器的电压电流相位进行计算，以此算出理想的频率跟踪步长和方向。最后通过MATLAB对算法进行仿真，验证算法在目标频率发生非线性变化时频率跟踪的效果。结果表明，新算法能够实现误跟踪的自复位和全状态频率跟踪，同时能在启动后10ms以内完成频率跟踪，跟踪精度达0.1hz。

Full-state frequency tracking algorithm of ultrasonic welding

Compared with ultrasonic plastic welding, ultrasonic metal welding load is heavy and changes dramatically, easily lead to no resistance point state of the transducer or frequency mis-tracking. Existing frequency tracking methods often only work properly when the transducer has a resistive point, and cannot be automatically reset in the event of mis-tracking. To address the above problems, this paper derives a frequency tracking algorithm based on the Mersenne equivalent circuit, which can be adapted to both resonant and anti-resonant frequencies and can determine whether the frequency tracking is mis-tracked. When the transducer is in the non-resistive point state, the algorithm will automatically change the tracking target to the minimum phase difference point to achieve full-state frequency tracking. The algorithm uses the three different frequencies and the voltage and current phases of the transducer when it emits waves to calculate the ideal frequency tracking step and direction. Finally, the algorithm is simulated by MATLAB to verify the effectiveness of the algorithm in frequency tracking when the frequency changes nonlinearly. The results show that the new algorithm can realize the self-resetting of false tracking and transducer state judgment, and the algorithm can complete the frequency tracking within 10ms after starting, and the tracking accuracy reaches 0.1hz.