Servo feed control for electrical discharge machining

Claim 2

In an electrical discharge machining apparatus for machining a conductive workpiece by passing electrical discharges from a tool electrode across a dielectric-collant-filled gap, a power supply, an electronic output switch operatively coupled between said power supply and said gap for providing machining pulses thereto, a triggering means for periodically turning said switch on, and at least one drive stage coupled between said triggering means and said switch, said drive stage operated out of phase with said switch and said gap, a servo feed system comprising a reversible motive means for providing relative movement between said electrode and said workpiece, an electrically energized element for controlling operation of said motive means responsive to direction of current flow through such element, a reference voltage source operatively connected to one terminal of said element, a sensing network connected between said gap and the other terminal of said element for providing a control voltage signal thereto representative of gap spacing, wherein the improvement comprises a network operatively connected between said drive stage and said element providing a voltage signal of downfeed polarity during said output switch off-time.

Claim 3

The combination as set forth in claim 1 wherein a second network is connected between said gap and said element to provide a control voltage signal of downfeed polarity during output switch on-time responsive to gap open circuit condition.

Claim 4

The combination as set forth in claim 1 wherein said first-mentioned sensing network comprises a series connected resistor and diode coupled between the output of said drive stage and said other terminal of said element.

Claim 5

The combination as set forth in claim 3 wherein said second network comprises a second series connected resistor and diode, connected between said gap and said other terminal of said element.

Claim 6

The combination as set forth in claim 4 wherein a differential amplifier is included, said amplifier comprising a first and a second transistor, each having a like principal electrode coupled to a different terminal of said element, said reference voltage source operatively coupled to the control electrode of one of said transistors and said networks both operatively connected to the control electrode of the other of said transistors.

Claim 7

The combination as set forth in claim 3 wherein said drive stage includes a PNP transistor having its collector operatively connected to the base of said output switch, said output switch also comprising a PNP transistor having its collector and emitter connected in series between said power supply and said gap.

Claim 8

In an electrical discharge machining apparatus for machining a conductive workpiece by passing electrical discharges thereto from a tool electrode across a dielectric-coolant-filled gap, a power supply, an electronic output switch having its principal electrodes connected in series between said supply and said gap for providing machining power pulses thereto, a servo feed contRol system for providing relative movement between said electrode and said workpiece including a reversible motive means and an electrically energized element for controlling operation of said motive means responsive to current flow through said element, and a reference voltage source operatively connected to one terminal of said element, wherein the improvement comprises a pair of sensing networks, both operatively coupled to the other terminal of said element, one of said pair comprising a diode, resistor and capacitor connected in series combination, said combination connected across said gap, and the other of said pair comprising a series-connected diode and resistor network, said network having one terminal connected to said gap.

Claim 9

In an electrical discharge machining apparatus for machining a conductive workpiece by passing electrical discharges thereto from a tool electrode across a dielectric-coolant-filled gap, a power supply, an electronic output switch having its principal electrodes connected in series between said supply and said gap for providing machining power pulses thereto, a servo feed contRol system for providing relative movement between said electrode and said workpiece including a reversible motive means and an electrically energized element for controlling operation of said motive means responsive to current flow through said element, and a reference voltage source operatively connected to one terminal of said element, wherein the improvement comprises a pair of sensing networks, both operatively coupled to the other terminal of said element, one of said pair comprising a diode, resistor and capacitor connected in series combination, said combination connected across said gap, and the other of said pair comprising a series-connected diode and resistor network, said network having one terminal connected to said gap.

Claim 10

The combination as set forth in claim 7 wherein said first of said pair of sensing networks includes a lead capacitor operatively connected between the terminal of said capacitor in common with said resistor and said element whereby an anticipation signal is provided to improve the response time of said servo feed system.

Claim 11

A servo feed system for an electrical discharge machining apparatus in which a conductive workpiece is machined by electrical discharges from a tool electrode across a dielectric-coolant-filled gap, comprising a reversible motive means for providing relative movement between said electrode and workpiece as material is removed from said workpiece, an electrically energized element operatively connected to and controlling the operation of said motive means responsive to current flow through said element, wherein the improvement comprises a reference voltage source operatively connected to one terminal of said element and a pair of sensing networks operatively connected to the other terminal of said element, for providing a combined control voltage thereto, said pair comprising a first sensing network for providing a voltage signal which is a function of gap striking voltage and a second sensing network for providing a voltage signal which is a function of gap cutting voltage.

Claim 12

A servo feed system for an electrical discharge machining apparatus in which a conductive workpiece is machined by electrical discharges from a tool electrode across a dielectric-coolant-filled gap, comprising a reversible motive means for providing relative movement between said electrode and workpiece as material is removed from said workpiece, an electrically energized element operatively connected to and controlling the operation of said motive means responsive to current flow through said element, wherein the improvement comprises a reference voltage source operatively connected to one terminal of said element and a pair of sensing networks operatively connected to the other terminal of said element, for providing a combined control voltage thereto, said pair comprising a first sensing network for providing a voltage signal which is a function of gap striking voltage and a second sensing network for providing a voltage signal which is a function of gap cutting voltage.

Claim 13

In an electrical discharge machining apparatus for machining a conductive workpiece by electrical discharges between a tool electrode and said workpiece across a dielectric-coolant-filled gap, a power supply, a periodically operated electronic switch coupled between said power supply and said gap for providing machining power pulses thereacross, a triggering means for turning said switch on and off with variable on-off time to initiate said pulses, and a drive stage coupled between said triggering means and said switch, said drive stage operable out of phase with said gap machining power pulses, a servo feed system for providing relative movement between said electrode and said workpiece including a reversible motive means and an electrically energized element for controlling operation of said motive means responsive to current flow through said element, a reference voltage source operatively connected to one terminal of said element and a gap voltage-sensing network operatively connected to the other terminal of said element, wherein the improvement comprises a pair of sensing networks, both operatively connected to said other terminal of said element, one of said pair connected to said drive stage and operable to provide a down-feed polarity signal to said element during machining pulse off-time and the other of said pair connected to said gap and operable to provide a down-feed polarity signal to said element during machining pulse on-time.

Claim 14

In an electrical discharge machining apparatus for machining a conductive workpiece by electrical discharges between a tool electrode and said workpiece across a dielectric-coolant-filled gap, a power supply, a periodically operated electronic switch coupled between said power supply and said gap for providing machining power pulses thereacross, a triggering means for turning said switch on and off with variable on-off time to initiate said pulses, and a drive stage coupled between said triggering means and said switch, said drive stage operable out of phase with said gap machining power pulses, a servo feed system for providing relative movement between said electrode and said workpiece including a reversible motive means and an electrically energized element for controlling operation of said motive means responsive to current flow through said element, a reference voltage source operatively connected to one terminal of said element and a gap voltage-sensing network operatively connected to the other terminal of said element, wherein the improvement comprises a pair of sensing networks, both operatively connected to said other terminal of said element, one of said pair connected to said drive stage and operable to provide a down-feed polarity signal to said element during machining pulse off-time and the other of said pair connected to said gap and operable to provide a down-feed polarity signal to said element during machining pulse on-time.

Claim 15

The combination as set forth in claim 10 wherein each of said pair of sensing networks comprises a series connected resistor and diode, said diodes like phased relative to said other terminal of said element.

Claim 16

The combination as set forth in claim 10 wherein said gap voltage-sensing network includes a diode, resistor and capacitor connected in series combination, said combination coupled across said gap for responding to a voltage which is a function of gap striking voltage.

Claim 17

The Combination as set forth in claim 12 wherein a parallel resistor-capacitor network is coupled between said first mentioned capacitor and said other terminal of said element for providing an anticipation signal thereto.

Claim 18

In an electrical discharge machining apparatus for machining a conductive workpiece by electrical discharges between a tool electrode and said workpiece across a dielectric-coolant-filled gap, a power supply, a periodically operated electronic switch having its principal electrodes connected between said supply and said gap for providing machining power pulses thereacross, and a triggering means for operating said switch with variable on-off times, a servo feed system for providing relative movement between said electrode and said workpiece, including a reversible motive means and an electrically energized element for controlling operation of said motive means responsive to a control voltage signal provided to one terminal of said element, wherein the improvement comprises a pair of sensing networks both operatively coupled to said terminal, one of said networks connected between said gap and said terminal for providing thereto a signal representative of gap peak voltage, the other of said networks connected between said gap and said terminal providing thereto a signal representative of gap cutting voltage whereby said element and said motive means are responsive to a combination of said signals.

Claim 19

In an electrical discharge machining apparatus for machining a conductive workpiece by electrical discharges between a tool electrode and said workpiece across a dielectric-coolant-filled gap, a power supply, a periodically operated electronic switch having its principal electrodes connected between said supply and said gap for providing machining power pulses thereacross, and a triggering means for operating said switch with variable on-off times, a servo feed system for providing relative movement between said electrode and said workpiece, including a reversible motive means and an electrically energized element for controlling operation of said motive means responsive to a control voltage signal provided to one terminal of said element, wherein the improvement comprises a pair of sensing networks both operatively coupled to said terminal, one of said networks connected between said gap and said terminal for providing thereto a signal representative of gap peak voltage, the other of said networks connected between said gap and said terminal providing thereto a signal representative of gap cutting voltage whereby said element and said motive means are responsive to a combination of said signals.

Claim 20

The combination as set forth in claim 14 wherein an amplifier stage is connected between said last-mentioned network and said element terminal for providing a weighted combination of said signals.

Claim 21

The combination as set forth in claim 15 wherein a parallel resistor-capacitor network is connected between said sensing networks and element terminal for decreasing the response time of said servo feed system.

Claim 22

The combination as set forth in claim 15 wherein a variable reference voltage source is operatively connected to the other terminal of said element and a rheostat is connected in parallel with said element for adjusting the gain of said system.

Claim 23

In an electrical discharge machining apparatus for machining a conductive workpiece by electrical discharges between a tool electrode and said workpiece across a dielectric-collant-filled gap, a power supply, a periodically operated electronic switch having its principal electrodes connected between said supply and said gap for providing machining power pulses thereacross, and a triggering means for operating said switch with variable on-off times, a servo feed system for providing relative movement between said electrode and said workpiece including a reversible motive means and an electrically energized element for controlling operation of said motive means responsive to a control voltage signal from said gap, provided to one terminal of said element, wherein the improvement comprises a pair of networks, one of said networks operatively connected between the input to said switch and said terminal to provide a down-feed polarity signal thereto during switch off-time and the other of said networks operatively connected between the output of said switch and said terminal providing a down-feed polarity signal thereto during switch on-time.

Claim 24

In an electrical discharge machining apparatus for machining a conductive workpiece by electrical discharges between a tool electrode and said workpiece across a dielectric-collant-filled gap, a power supply, a periodically operated electronic switch having its principal electrodes connected between said supply and said gap for providing machining power pulses thereacross, and a triggering means for operating said switch with variable on-off times, a servo feed system for providing relative movement between said electrode and said workpiece including a reversible motive means and an electrically energized element for controlling operation of said motive means responsive to a control voltage signal from said gap, provided to one terminal of said element, wherein the improvement comprises a pair of networks, one of said networks operatively connected between the input to said switch and said terminal to provide a down-feed polarity signal thereto during switch off-time and the other of said networks operatively connected between the output of said switch and said terminal providing a down-feed polarity signal thereto during switch on-time.

Claim 25

The combination as set forth in claim 18 wherein a unilateral current-conducting device and a capacitor are operatively connected across said gap and to said element terminal for providing said control voltage signal thereto, which signal is a function of gap striking voltage.

Claim 26

The combination as set forth in claim 19 wherein a means is operatively connected between said gap and said capacitor for providing a second signal which is a function of gap cutting voltage and adding it to said control voltage signal.