During the welding process on ultrasonic welder, the electrical signal input to the acoustic system changes quickly, and the frequency variation range is wide. In order to improve the measurement speed and accuracy, firstly, measures are taken to select the chip with fast response speed, and the time constant of the component and the filter link of the peripheral circuit of the chip is controlled to be less than 0.2 ms, so as to ensure the total response time of the system is less than 2 ms, and meet the demand of detecting the rapidly changing electrical signal. In order to ensure the requirement of wide frequency band amplitude and frequency characteristics of the system, RCK type resistor with high precision and high stability is selected, which has minimal parasitic inductance and capacitance. Op-amp components shall be selected with open-loop magnification of more than 10 and closed-loop magnification of less than 10. In this way, a flat amplitude-frequency curve can be obtained from 0 ~ 20 kHz ±3 kHz. The following is a brief description of each functional module.
1.1 Measurement of Vrms of voltage RMS
The test equipment developed in this paper can measure the sinusoidal voltage signal with distortion with RMS of 0 ~ 1 000 V and frequency of 20 kHz±3 kHz. The input voltage is extracted by signal, the RMS value is converted to AC/DC, and then proportionally adjusted into two output channels. One channel is supplied to the 3-bit semi-digital meter head on the front panel of the tester, which directly displays the RMS value of 0-1 000 V voltage. The other one outputs 0 ~ 10 V analog voltage signal through the back panel of the tester for data acquisition and analysis by the computer.
The voltage signal can be extracted by voltage transformer, Hall element sensor or photoelectric conversion device. These methods
Although the isolation is good, it will produce different degrees of waveform distortion and additional phase shift for the 20 kHz electrical signal, which makes it difficult to ensure the accuracy of power measurement and phase Angle measurement. This article USES the proportional amplifier to voltage signal processing, the amplifier input resistance using 5. 1 M Ψ, this aspect can make the input signal attenuation, high pressure protection for subsequent circuits, and as a result of the amplifier input impedance far outweigh the signal source resistance of ultrasonic generator, ultrasonic generator working status has no impact.
AD637 is used for voltage RMS measurement. It is an AC-DC RMS converter with high upconversion accuracy and wide frequency band, and the conversion is independent of the waveform. It is a true RMS converter. The maximum error is about 1%. When the waveform factor is 1 ~ 2, no additional error is produced.
1.2 Measurement of effective current value
The current RMS detection circuit developed in this paper can detect the current signal with sinusoidal distortion of 0 ~ 2 A, 20 kHz ±3 kHz. By adopting the standard sampling resistance connected in series to the load loop of the ultrasonic generator in FIG. 1, the current is first converted into voltage signal proportional to it. Since the sampling resistance is a pure resistive device, it will not bring current waveform distortion or additional phase shift, so as to ensure the measurement accuracy. The voltage signal proportional to current is converted into analog voltage signal by RMS AC-DC converter AD637, which is output to digital meter head and computer in two ways. The conversion principle is the same as that of RMS voltage conversion.
1.3 Measurement of active power
The active power measurement signal comes from the attenuated voltage and I/ V transformed signal in the RMS measurement module of voltage and current. The core of the power measurement module is AD534 analog multiplier and filter circuit. After the instantaneous voltage is multiplied by the current flow multiplier, the high-frequency component is filtered out to obtain the actual active power.
1. 4 Measurement of phase difference between current and voltage
The phase difference between the input voltage and current of the ultrasonic transducer is measured by shaping the input voltage and current signals into square waves through a zero-crossing comparator, and then synthesizing the phase difference through XOR logic processing. Because there is not only phase difference between voltage and current, but also the difference between lead and lag, Ming Yang also designed a timing circuit to identify the lead and lag relationship. If you have any need please contact us.
1.5 Frequency measurement
Frequency measurement module adopts single chip microcomputer 8051, using the standard crystal frequency, crystal pulse signal count in a certain signal period, can be realized within 1 ms, the frequency is 20 kHz, the error is not more than 2 Hz. The frequency measurement results are output by 16-bit binary numbers, input to the computer I/O card, and converted into decimal actual frequency values by software programming.
Ultrasonic plastic welding is completed under instantaneous and pressure, and the welding process shows the characteristics of fast, complex, difficult and multi-parameter influence. During and after welding, considerable stress and deformation (welding residual deformation, welding shrinkage, welding warping) will be produced, and the dynamic stress and welding residual stress generated in the welding process, but also affect the deformation of the workpiece and welding defects.
It also affects the weldability of the workpiece structure and the brittle fracture strength, fatigue strength, yield strength, vibration characteristics and so on. Especially affect the welding workpiece machining accuracy and dimensional stability. The problem of welding thermal stress and deformation is very difficult, without foresight, can not comprehensively predict and analyze the influence of welding on the mechanical properties of the whole welder, and objectively evaluate the welding quality. At the same time, many important data, namely impact, cannot be measured directly by conventional methods.
We are a professional R & D, production, and sales of ultrasonic welding machine, high frequency welding machine, metal welding machine, Ultrasonic generator factory. We are happy to share our ultrasound technical support and ultrasound case experience. If you have a project to consult, please tell us the material and size of your products. We will provide you with a free ultrasonic welding program.
Post time: Oct-20-2022