Stochastic events - a requirement for the control of complex processes

All welding processes as well as processes of thermal spraying of any kind, whether hand-held or robot-controlled, must be controlled very precisely and flexibly.

Physical parameters, e.g. the material type of the materials to be welded, material thicknesses, current, voltage, wire feed, electrode forces, coating thicknesses, addiditves, process gas flow and time have to be optimally matched in different applications and also different welding technologies.

For example, in arc wire spraying the requirements vary up to an extremely individual and fine process management. At the same time, the exact reproducibility of these complex processes (process reliability) must be ensured in industrial applications.

The problem of controlling such process types

Controlling the physical quantities occurring in these processes, such as current and voltage of an electronic generator, is difficult because they are not exactly deterministic due to the complexity or degrees of freedom of the process - they are therefore stochastic (random) events in a certain context.

Process control with fixed characteristic curves only yields average values in the best case and can not react to stochastic changes in individual process phases. One could say that fixed characteristic curves do not allow „sensitive“ and customizable management of processes.

The solution: welding control with "virtual machine"

The individual process states during welding or thermal spraying are subdivided into discrete time units or segments. One basic idea is to be able to segment a process with start and end into individual areas (start, stationary area, exit), another to be able to react within a segment to process peculiarities with replacement of the generator characteristics as soon as possible.

Via the computer system of the virtual machine, those parameters which define the static and dynamic generator behavior are exchanged as often and as quickly as possible, so that a generator can be provided, which is optimally suited for each identifiable process phase.

This subdivision process into smallest time units is repeated according to the requirements of the respective welding task until the completion of the welding operation. The static and dynamic control implemented in the Virtual Machine evaluates these rapidly changing process states.

These are processes that take place in the thousandths of a second range. The Virtual Machine responds to any different condition within the range of its cycle frequency of 20 kHz, that is within 50 microseconds. The limit of the reaction time of 50μs already results from the technical possibilities to enforce modified action of the generator over connecting lines to the process. Each line between generator and sink (process) has inductive components that do not require a higher rotational speed of the slave processor, as an enforcement above 10 kHz can not succeed anyway.

Also other controls are practically replaced by the Virtual Machine: With such a structure, not only the generator character of the power source can be redefined, but also all other and peripheral controls of e.g. servo valves in welding guns or wire feeds in arc processes can be carried out.

More details

Benefits of the Virtual Machine in ELMA-Tech spot welding machines
Benefits of the Virtual Machine in ELMA-Tech arc welding machines
Benefits of the Virtual Machine in ELMA-Tech Aluminum spot welding systems