The purpose of the thesis is to develop a new user interface for inverter welding device. The development of a new user interface began on an existing iMIG 250 device.
In order for the device to function properly, it was first necessary to obtain values and shapes of control signals that control the power output of the device. Device allows welding in two different modes of operation. It was necessary to obtain the corresponding values of the control signals for each mode of operation. In case of output power control, the control signal is shown to be unidirectional and its value increases or decreases linearly. On a existing device the output power is controlled via a 4.7 kΩ resistive potentiometer, which has been replaced by rotary encoder and an eight bit D/A converter. Instead of continuous adjustable voltage, the output power of the device is now controlled by the new circuit that generates a limited number of discrete DC voltage.
A 50 kΩ potentiometer is used to set the welding characteristic. The value of the potentiometer affects the shape of the weld. If the potentiometer value is lower, the weld is firmer, but if the potentiometer value is higher, then the weld is softer. When the welding machine was upgraded with new user interface, the 50 kΩ potentiometer was replaced by a resistor chain. This resistor chain consists of eight resistors and its desired total resistance is set of four-bits resolution by means of transistors and relays. The relays are used to vary the resistance of the entire circuit by short-circuiting appropriate resistors.
Initially, new hardware, consisting of TFT display and new CS3051 circuit, was installed to generate appropriate control signals in order to comply with the user preferences. The output power of the device is controlled by an analog circuit that generates a pulse width modulated signal. When setting the desired value of the welding voltage or the desired value of the welding current, communication between the TFT screen and the device now takes place via the digital bus. The existing program which controls the inverter part of the device, was modified and upgraded. The program was created in the Realizer Gold software environment. The existing program was upgraded with a program code for the control of the TFT display. Certain variables and parameters were also modified and updated in order to generate the appropriate control signal.
Initially, one iMIG 250 GR test rig was made and is still in use for testing purposes in order to identify and correct minor failures in functionality. In the current stage, these failures are corrected only by the modifications of the program. After major errors were rectified, another sample of welding machine was built and sent to the customer for a performance verification.