Adaptive control for spot welding

More and more, adaptive or intelligent controls are finding their way into modern manufacturing. So what is the difference between such systems and the classic and well-known constant current control?

Here is the basic definition of a regulation. In a closed-loop control system, the variable to be controlled (controlled variable x) of a process is continuously measured and compared with a specified value (setpoint or reference variable w). If there is a deviation between these two variables (control difference or control error e or control deviation xw), a manipulated variable (u) influencing the process is changed depending on the control deviation in such a way that the controlled variable is brought back into line with the reference variable.

With the constant current control (or also called), the secondary welding current is kept constant due to a predefined setpoint. In less demanding applications, this can also be the primary current. The decisive factor is that the current is controlled according to a fixed value or slope in accordance with the controlled variable to the reference variable.

Adaptive or intelligent control is characterised by the fact that there is no constant default, but reacts according to the values measured online, usually current and voltage, and the values calculated from them, usually resistance or power, during the actual welding and a reference variable is interpolated discretely in time according to internal know-how (model conception dependent on the material).

In other words, the reference variable is not constant or has a predefined form, but is variable according to the currently prevailing boundary conditions of the specific weld, taking into account stored know-how (expert knowledge) about the material.
Such an adaptive system is, for example, the IQR control for the Genius inverter series, which, based on the proven constant current control, takes up these possibilities of adaptive control in order to compensate for the known weaknesses of pure constant control.