EDM Power Supply Switching Control for Low-Ripple Discharge
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Solution Overview
Problem
Conventional power supply devices for electric discharge machines face issues with current ripples, leading to electrode degradation, increased heat generation, reduced machining speed, and abnormal arc discharges, particularly when attempting to reduce ripples through higher switching frequencies or high inductance smoothing inductors.
Innovation Solution
A power supply device with multiple switching elements in parallel, a current value acquisition unit, and an ON-OFF control unit that synchronizes switching cycles and ON-periods based on current values, eliminating the need for high inductance smoothing inductors and distributing heat loss, thereby reducing current ripples and preventing abnormal arc discharges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the switching frequency of the switching element is increased to reduce current ripples, then current ripple is reduced, but switching loss increases and heat generation increases
Solution Approach 1:
The patent divides a single switching element into multiple switching elements (first switching element and second switching element) that operate in parallel with different switching frequencies. The first switching element switches at a higher frequency while the second switches at a lower frequency, segmenting the total current ripple reduction task among multiple elements with different characteristics. This allows the system to achieve effective current ripple suppression without concentrating all switching losses in a single element, thereby reducing overall heat generation.
2Manufacturing precision
If a smoothing inductor having a high inductance value is arranged in the cable to reduce current ripples, then current ripple is reduced, but the workpiece machining speed is reduced due to the lengthening of the time from the start of current until peak current is reached
Solution Approach 1:
The patent replaces the mechanical/physical approach of using a high inductance smoothing inductor with an electronic control approach using multiple switching elements with different switching frequencies. Instead of relying on the inductive reactance of a large inductor to suppress current ripple, the system uses coordinated switching of multiple elements to achieve ripple suppression. This eliminates the need for large inductance values that would otherwise slow down current rise time and reduce machining speed.
3Manufacturing precision
If a smoothing inductor having a high inductance value is arranged in the cable to reduce current ripple, then current ripple is reduced, but the time from the start of current fall until the current value reaches zero becomes long, whereby an abnormal arc discharge may occur
Solution Approach 1:
The patent segments the current control function across multiple switching elements with different switching frequencies and phases. The first switching element operates at a higher frequency to suppress current ripple during the current rise and peak phases, while the second switching element operates at a lower frequency to control the current fall phase. This segmented approach allows independent optimization of each phase, ensuring that current falls to zero quickly and reliably without the prolonged current tail that would cause abnormal arc discharge.
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 effectively reduces current ripples, minimizes heat generation, maintains machining speed, and prevents abnormal arc discharges by distributing switching losses among multiple elements and optimizing switching cycles, without requiring high inductance inductors.
Implementation Method 1
a DC power supply which is connected in parallel to the electrode gap for applying a voltage for generating the current to the electrode gap
Implementation Method 2
a plurality of switching elements which are in parallel to each other and which are arranged between the electrode gap and the DC power supply
Implementation Method 3
for supplying a pulsed current to an electrode gap constituted by a workpiece and an electrode, which are opposed to each other with a predetermined gap, for electric discharge machining a workpiece
Data Source
AI summary
A power supply device for an electric discharge machine includes a DC power supply which is connected in parallel to an electrode gap, a plurality of switching elements which are in parallel to each other and which are arranged between the electrode gap and the DC power supply, a current value acquisition unit for acquiring a value of a current, and an ON-OFF control unit which, during the time when the current value reaches a predetermined value until the time when the current starts to fall, sets a cycle for switching the plurality of switching elements from off to on to the same cycle, switches the plurality of switching elements from off to on in a predetermined order for each timing of a phase of 90°, which is 360° divided by the number of the plurality of switching elements, sets an ON-period of each of the plurality of switching elements based on a difference between the value of the current and the predetermined value, and performs ON-OFF control of the plurality of switching elements based on the cycle, the timing, and the ON-period.