Basic principle of automatic frequency tracking ba

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Basic principle of current feedback frequency automatic tracking

in ultrasonic machining, the changes of temperature, material stiffness, static load, sintering process, machining roughness, tool wear and load force of piezoelectric transducer make the inherent resonant frequency of piezoelectric transducer drift, and the vibration system will work in a non resonant state, so that the transmission amplitude of the vibration system is reduced, resulting in the decline of machining quality. Therefore, whether the vibration system can always be in the resonant state is the key to the smooth progress and quality of ultrasonic machining. In practical application, the power frequency of the transducer should be adjusted in time, otherwise the frequency adjustment used in the working mode is not only inefficient, but also does not meet the requirements of automatic production. Therefore, it is necessary for the generator to have the performance of automatic frequency adjustment, that is, the so-called automatic frequency tracking

the current of the main circuit of the ultrasonic power source, the amplitude A of the vibration of the transducer and the frequency f of the ultrasonic generator correspond monotonously, as shown in Figure 1. When the transducer resonates, the amplitude is the largest, and the current of the main circuit is also the largest. As the demand for the control variable instrument continues to grow with the current round of global air transportation and general aviation services to resolve the policy objective of excess capacity, the instrument is the relationship between the frequency of the ultrasonic generator and the current input to the inverter circuit (which directly reflects the amplitude of the transducer vibration system), while the products currently produced by ultrasonic include the spring testing machine series, and the frequency of the generator has a monotonic corresponding relationship with the vibration amplitude A of the transducer, So this is a univariate linear programming problem. Let I be the target to be searched and f be the influencing factor. First, the corresponding I2 is obtained according to the progressive amount △ F of F within the allowable range. Compare IL with I2. If I1 12, it means that I is increasing, continue to advance in the original direction to get I3, I4... If nf5, the value of I decreases, it means that the control exceeds the limit point, and the progression should change the direction. In this way, the current value with arbitrary accuracy can be obtained as long as the number of progressive steps is increased (or reduced). Repeating the above process every certain time can ensure that the system can adapt to the change of load and make the system work in a resonant state

by analyzing the actual application process, it can be seen that "the main factors affecting the amplitude (such as load) It is stable in a certain period of time, so if the working speed of the system is fast enough, the maximum current value of the main circuit can be searched in this period of time, and the resonant frequency point can be found. The frequency tracking system of single chip microcomputer adopts the frequency conversion search mode, so that the current of the main circuit is always kept at the maximum value, so as to ensure that the whole acoustic system always works in the resonant state

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