In order for the robot to weld properly, it has to be given some intelligence, which is provided through a software interface that takes care of the communications between the robot controller and the power sources. The typical control over the welding process includes these functions:
Gas pre-flow and post flow
Start & end voltage with time
Main seam voltage or trim if in synergic mode
Main seam wire feed speed
Start & end wire feed speed
Pulse patterns trim
Burn back control
Automatic re strike
In the early days of robot welding most of these parameters had to be programmed by the robot programmer, who therefore needed to understand the affect on the welding process, how to achieve the functionality by programming various parameters in the robot controller and above all understand the welding process. The settings were made from the teach pendant and the process became quite complicated, which meant that in some challenging applications, a robotic welding engineer was responsible for programming the robot.
Since then there has been a shift change in technology and the power source is now able to hold and control the majority of parameters, which are largely automatically optimised using synergic lines through built in welding software. Of course the programmer still needs a fairly good understanding of the welding process, but it is a lot easier and faster to get good results. The welding parameters tend to be stored inside the power source as a series of schedules containing various parameters, that are needed to achieve good results for any given joint. The schedules are simply selected by the programmer and then selected from the robot to the controller via digital interface.
One of the advantages of this kind of interface is that it is easier to identify any faults since the tasks are clearly identified with the robot being responsible for moving the torch and the power source being responsible for the process. This principle of interface works as follows:
At the start of the joint the robot controller sends a digital output to the power source to select a particular weld schedule (start, main and end conditions).
The robot controller then initiates a signal for the power source to switch on the welding process.
The robot power source returns a signal to the robot controller that an arc has been established.
The robot controller then initiates the movement of the robot.
At the end of the joint the robot sends a signal to the power source to stop the process and extinguish the arc.
The robot moves to the next position in its program, etc.