Unipulse Plasma Torch Ignition Circuit
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Solution Overview
Problem
Conventional plasma cutting tools face issues with RF interference and increased complexity due to high-frequency, high-voltage signals used for arc initiation, which can lead to operational problems and compliance challenges with regulations.
Innovation Solution
A plasma starting system that initiates a pilot arc using a single unipolar high voltage impulse, eliminating the need for a spark gap assembly and associated RF noise, and preloading the power supply inductor to maintain the arc without surge injection circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-frequency, high-voltage signals are used to initiate the plasma arc, then arc ignition is achieved, but RF interference is introduced causing operational problems and compliance challenges
Solution Approach 1:
The patent changes the electrical parameters of the ignition signal from high-frequency alternating current to low-frequency unipolar pulses (e.g., 1-100 Hz versus conventional 20-100 kHz). This parameter change maintains arc ignition capability while eliminating RF interference, as the unipolar pulses do not generate the electromagnetic radiation problems associated with high-frequency AC signals
Solution Approach 2:
Instead of using the conventional approach of applying high-voltage across the power source terminals through a spark gap, the patent inverts the approach by injecting the ignition pulse in series with the power source output. This inversion allows the pulse to be applied without imposing high voltage across the power source terminals, eliminating the need for blocking components and reducing RF interference
2Reliability
If conventional high-frequency starting circuits are used, then arc ignition is achieved, but additional bypass or blocking components are required increasing device complexity
Solution Approach 1:
The patent extracts and eliminates the spark gap assembly and associated RF noise-generating components from the system. By using unipolar pulse injection instead of high-frequency AC through a spark gap, the design removes the need for bypass or blocking capacitors and other RF filtering components, simplifying the power supply circuit while maintaining reliable arc ignition
Solution Approach 2:
The patent inverts the conventional connection topology by injecting the ignition pulse in series with the power source output rather than in parallel across the terminals. This topological inversion allows the ignition circuit to share the power source inductor without requiring additional blocking components, thereby reducing device complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution reduces RF noise, simplifies the power supply design, and eliminates the need for additional circuitry, resulting in a more reliable and cost-effective plasma cutting process with improved arc initiation and maintenance.
Implementation Method 1
Once the gas ionizes, a glow discharge results and the inductor current transfers from the start circuit to the torch pilot arc circuit to maintain the arc
Implementation Method 2
The impulse starting circuit can be powered from the power source output and as such preloads the output inductor of the power source. Once the gas ionizes, a glow discharge results and the inductor current transfers from the start circuit to the torch pilot arc circuit to maintain the arc
Data Source
AI summary
A starting circuit for use with a plasma torch is provided including circuitry for initiating a pilot arc using a unipolar voltage impulse. A transformer is selectively coupled to a DC source so that an impulse is introduced using the same DC source used to maintain an established pilot arc. A method is provided wherein an arc can be initiated while at the same time the DC source is pre-loaded so that surge injection circuitry is not needed to sustain the arc while ramping to the full pilot arc current level.