The development of the electrode displacement detection system for medium frequency spot welding machines has rapidly evolved in recent years. It has progressed from simple displacement curve recording or basic instrumentation to sophisticated control systems involving data processing, alarm functions, and feedback control. The basic detector consists of sensors, amplifiers, comparators, displays, and other components.
These simple instruments are cost-effective but lack precision and feedback control, limiting their applicability. Therefore, they are rarely used nowadays. Microprocessor-controlled systems, on the other hand, consist of displacement sensors, encoders, displacement feedback interfaces, central processing units, and displays. This system enables real-time feedback and emerged in the late 1970s.
Displacement sensors come in various forms such as mechanical, potentiometric, capacitive, inductive, and grating. The selection depends on measurement accuracy, ease of use, and cost. Currently, most systems employ inductive and grating sensors.
Axial differential inductance sensors comprise two inductive coils, a magnetic pole, miniature steel columns, guide sleeves, and adjusters. These coils are differentially connected to the inductance meter’s bridge. The meter’s oscillator outputs a stable high-frequency voltage, applied across the inductive coils, magnetic pole, miniature steel columns, guide sleeves, and adjusters.
When the magnetic pole is at the center (i.e., displacement is zero), the inductance of both coils is equal, resulting in a balanced bridge and zero output voltage. As the magnetic pole displaces, the inductance of one coil increases, while the other decreases, causing the bridge to become unbalanced and generate an output voltage proportional to the displacement. The polarity of the output voltage indicates the direction of the displacement. Actual products, like the GCH-1, generate output voltage across the bridge, which is then amplified and demodulated to obtain displacement values. Phase-sensitive demodulation is used to ensure the characteristic curve of the rectified bridge current crosses the zero point, eliminating residual voltage.
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Post time: Apr-08-2024
