System for Keeping Constant The Torch - Material Distance In Machines for Oxygen-Gas Or Plasma Cutting

The system for keeping constant the torch - material distance in machines for oxygen-gas or plasma cutting consist of torch holder, DC servo motor drive with dynamic overcurrent protection, limit switches, four channel capacitive height measurement sensor, interface PCB, microprocessor based controller with digital display and key pad and system power supply. The digital display shows heights in the range 2,0 - 99,9 mm with 0,1 mm resolution. The four button key pad allows adjustment of all the process parameters using P algorithm of control, working mode choice and keeping all process parameters in EEPROM. It is provided full duplex RS 232C interface for computer linking, optoisolated inputs "Start" and "Hold" and optoisolated output "Ready", signalizing reaching the set point.

The four channel sector capacitive height measurement sensor provides torch positioning with accuracy, better than 0,2 mm even in the corner of the cutting sheet. The four independent channels are scanned every 200 us and output signal is proportional to the smallest measured height magnitude. To avoid the static error in positioning using P algorithm of control, it is provided adjustment of the minimum value of PWM output. It is realized procedure for everyday autocallibration of the measuring electronics to minimize the thermal and geometry influences. This procedure is manually started and it is binding on turning to working modes.

In the "Oxygen-gas cutting" mode of operation the positioning and keeping constant the set point height is provided by negative feedback signal from the height sensor continuously. In the "Plasma cutting" mode only the positioning is provided by negative feedback signal from the height sensor. After the plasma ignition the item measures the arc discharge voltage, memorizes it in the processor memory and keeps it constant by changing the torch to material distance. Thus the system provides constant arc current magnitude and good cut-off quality.

When the system works the display shows the active working mode of operation and current distance in "Oxygen-gas cutting" mode or arc discharge voltage in "Plasma cutting" mode. While the system works, if the torch pushes the lower limit switch, the display shows "Alr" and the torch goes up to upper limit switch. To restart working it is necessary to make zero the "Start" signal and restart the system again.

It is provided manual height control by choosing "Manual" mode. In this mode the torch is moving by pressing "Up" or "Down" buttons. When the torch pushes one of the limit switches, the motion in this direction restricts and the torch can moves only in the reverse direction.

Above mentioned system for keeping constant the torch - material distance in machines for oxygen-gas or plasma cutting provides the possibility of full automation of the cutting processes and guarantee excellent cut-off quality including near to sheet end. It is possible to append additional modules and functional capabilities by customer requirement.

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