Wire EDM Voltage Detection Using Segmented Pulse Off Periods
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Solution Overview
Problem
High-frequency AC voltage machining in electric discharge machining faces challenges in precise detection of machining state, leading to measurement errors and reduced machining accuracy due to disturbances from voltage variations and sludge accumulation, which complicates electrode feed rate control.
Innovation Solution
A wire electric discharge machine is configured to apply positive and negative voltages for short durations with an off time, incorporating a detection system to count voltage application cycles, open-circuit, electric discharge, and short-circuit states, allowing for accurate calculation of average machining voltage based on predetermined voltage levels, enabling precise control of electrode feed rate and machining conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high-frequency AC voltage is used for machining, then fine machined surface can be obtained, but it is difficult to precisely detect the machining state
Solution Approach 1:
The patent segments the continuous high-frequency voltage waveform into discrete pulse cycles, with each cycle containing a voltage application period and an off period. This segmentation allows the detection system to measure parameters during the off period when the high-frequency interference is absent, thereby resolving the contradiction between achieving fine surface finish with high-frequency voltage and enabling precise machining state detection.
2Manufacturing precision
If high-frequency AC voltage of several MHz or more is used, then fine machining can be achieved, but the response of detection circuit is degraded causing serious measurement errors
Solution Approach 1:
The patent implements periodic action by alternating between voltage application periods and off periods in a cyclic manner. During the off period, the detection circuit measures the machining gap voltage without interference from the high-frequency voltage application, enabling accurate detection of average voltage and machining state. This periodic switching resolves the contradiction by providing dedicated measurement windows free from high-frequency interference.
3Manufacturing precision
If average voltage detection is used for electrode feed control, then high-precision machining shape can be obtained, but the electrode feed rate must be made constant hindering improvement in machining accuracy
Solution Approach 1:
The patent applies dynamics by enabling the electrode feed rate to vary dynamically based on real-time detection of machining state parameters during the off period. The system calculates average voltage and discharge characteristics from periodic measurements and adjusts the feed rate accordingly, allowing optimization of both machining precision and productivity through adaptive control rather than constant feed rate.
4Measurement precision
If DC voltage is superposed on high-frequency AC voltage, then low-frequency voltage ingredient can be extracted, but electrolytic corrosion may occur and response is too poor for sudden changes
Solution Approach 1:
The patent extracts the necessary measurement information (average voltage and machining state) directly from the high-frequency AC waveform during the off period, without adding DC voltage or using low-pass filters. This extraction method avoids the harmful side effects of DC superposition such as electrolytic corrosion, while still providing the measurement precision needed for accurate machining state detection and control.
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 approach enables high-precision finish machining by accurately determining machining states and controlling electrode feed rate, even under conditions affected by disturbances, thereby improving machining accuracy and reliability.
Implementation Method 1
a voltage is applied to an electrode in a working fluid and a workpiece, thereby generating arc discharge
Implementation Method 2
The moment the workpiece is melted by heat generated by the electric discharge
Implementation Method 3
the working fluid is heated and explosively vaporizes, thereby blowing off melted portions of the workpiece
Implementation Method 4
an average of absolute values of machining-gap voltages is measured to determine the machining state
Data Source
Figure 1
Figure 2A~2C
Figure 3A~3C
AI summary
In order to detect a machining state of a wire electric discharge machine, the state of a machining gap is classified into three categories; an open-circuit state in which electric discharge does not occur after a first predetermined level (V1) is reached or surpassed by a machining-gap voltage, an electric discharge state in which electric discharge occurs after a second predetermined level (V2) is reached or surpassed by the machining-gap voltage, whereby the machining-gap voltage becomes lower than the second predetermined level, and a short-circuit state wherein a third predetermined level (V3) is not reached or surpassed by the machining-gap voltage. An average voltage in the machining gap is determined based on voltages in these states and the number of cycles of voltage application to the machining gap, number of open-circuits, number of discharges, and number of short-circuits per unit time.