US3749877A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Electrical arc detector
Assignee: ELECTRONIC REMOVAL OF METALS I
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Filing: 1972-01-11
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Granted: 1973-07-31
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Expires: 1992-01-11
Abstract
Abstract An electrical discharge machining circuit for sensing the failure of the arc current to extinguish between power pulses due to a direct current component in the arc current. The direct current component may be caused by leaky or shorted output transistors, by excess arc inductance for the power pulse duty factor, drive failure, or other causes. The direct current component causes ''''arc-out'''' damage to the workpiece and to the tool electrode. The circuit depends upon the drop-out point of a relay when the arc current duty factor approaches or includes a direct current component which component is used to oppose or cancel the relay holding current.
Inventors
- 👤 W Lobur
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 21:15
CPC Classifications
B; B23; B23H; B23H1/00; B23H1/02; B23H1/026
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
168 words
In an apparatus for machining a conductive workpiece by means of electrical discharges across a gap between said conductive workpiece and a tool electrode, including a source of machining power, an electronic control device having a control electrode and a pair of power electrodes, said power electrodes being connected between said source of machining power and said gap between the conductive workpiece and the tool electrode for providing electrical machining pulses thereto, and a drive signal means connected to said control electrode of said electronic control device for rendering said electronic control device alternately conductive and non-conductive, wherein the improvement comprises: current-sensing means operatively connected to said gap between said conductive workpiece and said tool electrode for sensing failure of extinguishment of arc current across said gap only when said electronic control device has been rendered nonconductive; and control means operatively connected to said sensing means for de-energizing said source of machining power when said failure of extinguishment of said arc current is sensed by said sensing means.
Claim 2
Dependent Claim
168 words
In an apparatus for machining a conductive workpiece by means of electrical discharges across a gap between said conductive workpiece and a tool electrode, including a source of machining power, an electronic control device having a control electrode and a pair of power electrodes, said power electrodes being connected between said source of machining power and said gap between the conductive workpiece and the tool electrode for providing electrical machining pulses thereto, and a drive signal means connected to said control electrode of said electronic control device for rendering said electronic control device alternately conductive and non-conductive, wherein the improvement comprises: current-sensing means operatively connected to said gap between said conductive workpiece and said tool electrode for sensing failure of extinguishment of arc current across said gap only when said electronic control device has been rendered nonconductive; and control means operatively connected to said sensing means for de-energizing said source of machining power when said failure of extinguishment of said arc current is sensed by said sensing means.
Claim 3
Dependent Claim
65 words
The combination according to claim 1, wherein an electrical component is connected between said source of machining power and one of said power electodes of said electronic control device, said electrical component having a substantially low impedance to the flow of electrons in a predetermined direction and having a substantially high impedance to the flow of electrons in a direction opposite to said predetermined direction.
Claim 4
Dependent Claim
32 words
The combination according to claim 1, wherein said control means includes the coil of a relay having its contacts operatively connected to and controlling the output from said source of machining power.
Claim 5
Dependent Claim
79 words
The combination according to claim 2, including a second electronic control device connected in parallel with the coil of said relay; said sensing means includes a dropping resistor connected in series with the arc loop containing said gap between said conductive piece and said tool electrode; a third electronic control device operatively connected to said sensing means and said second electronic control device for faithfully transferring the voltage drop appearing across said resistor to said second electronic control device.
Claim 6
Dependent Claim
75 words
The combination according to claim 2, wherein said sensing means includes an impedance element connected in series with said source of machining power, said electronic control device, and said gap between the conductive workpiece and the tool electrode; wherein the de-energization of said source of machining power depends upon the drop-out point of said relay coil when said arc current includes a direct current component which component is utilized to oppose the relay holding current.
Claim 7
Dependent Claim
38 words
The combination according to claim 1, wherein said sensing means includes an impedance element which forms part of a series circuit with said source of machining power, said electronic control device, said conductive workpiece, and said tool electrode.
Claim 8
Dependent Claim
95 words
The combination according to claim 9, wherein: said drive signal means is connected between one terminal of said source of machining power and said control electrode of said electronic control device; said electronic control device constituting the output transistor for the electrical discharge machining apparatus; one of said power electrodes of said output transistor being directly connected to one terminal of said impedance element, and said control means de-energizes said source of machining power when the non-conductive periods of said electronic control device are much shorter than the conductive periods of said electronic control device.
Claim 9
Dependent Claim
57 words
The combination according to claim 1, wherein said control means includes a relay coil having its contacts operatively connected to and controlling the output from said source of machining power; and including a source of direct current which is operatively connected to said relay coil and to one of said power electrodes of said electronic control device.
Claim 10
Dependent Claim
70 words
The combination according to claim 4, wherein said sensing means includes a dropping resistor connected in series with the arc loop which includes said gap between said conductive workpiece and said tool electrode, and said relay coil has a DC holding current which is responsive to ON-OFF ratio or duty factor of a square wave pulse that is opposed by a voltage derived as a function of said arc current.
Claim 11
Dependent Claim
28 words
A combination according to claim 4, including a fail-light ohmic indicator forming part of a circuit connected between said electronic control device and said source of direct current.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-07-30 | 1977-01-29 | 1977-07-31 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-07-30 | 1981-01-29 | 1981-07-31 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-07-30 | 1985-01-29 | 1985-07-31 | $7700.00 | Window Closed / Lapsed |