US3400207A

US3400207A - Apparatus for regulating power applied to an electron gun employed in an electron beam furnace

Info

Publication number: US3400207A
Application number: US399761A
Authority: US
Inventors: Emmett R Anderson
Original assignee: Temescal Metallurgical Corp
Current assignee: Temescal Metallurgical Corp
Priority date: 1964-09-28
Filing date: 1964-09-28
Publication date: 1968-09-03
Anticipated expiration: 1985-09-03
Also published as: DK115563B; DE1565145B2; SE337434B; BE670222A; CH448306A; GB1068119A; NL6512417A; DE1565145A1; JPS461385B1; AT267015B; FR1454584A; LU49502A1

Description

3 19.121 512 CRQ SS H MTRM- KR 3 a400;20-7

Sept. 3, 1968 E. R. ANDERSON 3,

APPARATUS FOR REGULATING POWER APPLIED TO AN ELECTRON GUN EMPLOYED IN AN ELECTRON BEAM FURNACE Filed Sept. 28, 1964 United States atcnt 3,400,207 APPARATUS FOR REGULATING POWER APPLIED TO AN ELECTRON GUN EMPLOYED IN AN ELECTRON BEAM FURNACE Emmett R. Anderson, Berkeley, Calif., assignor to T emescal Metallurgical Corporation, Berkeley, Calif., a corporation of California Filed Sept. 28, 1964, Ser. No. 399,761 7 Claims. (Cl. 13-31) ABSTRACT OF THE DISCLOSURE A power supply for an electron gun in an electron furnace is provided which power supply limits the voltage supply to the electron gun by employing a current control device as a series regulator to control the output of high voltage DC. power supply. The voltage signal developed across the electron gun is sensed by a voltage responsive means and output thereof is applied to a comparison means which amplifies the portion of the voltage signal which is greater than a predetermined reference voltage. The current passing through the electron gun issensed by a current responsive means, the output of which is coupled to the comparison means. The comparison means amplifies the portion of the current signal which exceeds the predetermined reference voltage. The current signal and the voltage signal are adjusted so that during normal operation of the electron beam gun, the amplitude of the current signal is less than the reference voltage and the voltage signal is larger than the reference voltage. During normal operation, the comparison means only amplifies a signal related to the voltage signal. It the beam current signal exceeds the reference voltage, which normally results from arcing in the electrostatic field of the electron gun, the comparison means amplifies the signal related to the current signal. The voltage signal during the maximum current operation is not amplified by the comparison means. The output signal of the comparison means is applied to a control element which controls the current passing through the current control device in an inverse relation to the signal controlling the comparison means.

The present invention relates generally to power supplies and more particularly to a regulated power supply capable of supplying several kilowatts of power to an electron beam gun employed in a high vacuum electron beam furnace.

Electron beam furnaces have been employed for various material-treating processes such as melting, anneal ing, cleaning, vapor-plating, etc. Normally, an electron beam apparatus includes an electron gun which provides and directs a beam of electrons at the material to be treated, the material being treated and the electron gun being enclosed in an evacuated chamber. The electron gun normally includes a source of electrons, such as a heated cathode or filament, and an anode which is main tained at a high positive potential relative to the cathode thereby establishing a high electrostatic field for accelerating the electrons. A focusing electrode is normally provided in the electron gun for focusing the electrons into a beam. The beam electrons bombard the workpiece and heat the same. The amount of heat developed in the workpiece is related to the electron beam current and the electron velocity resulting from the electrostatic field through which the electrons travel (i.e., voltage across the beam).

When the electrons bombard the workpiece, gases and vapors of various kinds are emitted by the heated material. These gases result in a decrease in the resistance of the path of the electrons which results in an increase in the electron beam current and, in fact, may result in arc discharges in the electrostatic field.

Generally, in previously available power supplies for electron beam furnaces only the electron beam current has been controlled or maintained constant, the current being adjusted for various treating processes. In such constant current power supplies a constant alternating current is produced which is rectified by a high voltage rectifier to provide a constant direct current. The direct current output of the rectifier is connected across the electron beam emanating from the electron gun and impinging on the workpiece. The electron beam thus is the load on the constant current network. The voltage developed across the electron beam depends upon the electron beam resistance. In certain previously available power supplies for electron beam furnaces, the voltage developed across the beam has been adjusted by controlling the filament temperature of the electron gun.

Normally, the constant current power supplies have been of the monocyclic type. Monocyclic power supplies generally include inductors and capacitors which are connected so as to provide resonant circuits which resonate at the frequency of the input circuit. Such circuits have ordinarily been provided with extensive circuits for protecting the various network elements from being overstressed when the electron beam furnace is operated over the extent of the desired output current range. Moreover, such networks require the provision of reactive elements of uneconomical large size.

It is an object of the present invention to provide an improved regulated power supply capable of supplying several kilowatts of power to the electron beam gun employed in a high vacuum electron beam furnace.

Another object of the invention is the provision of a power supply for an electron beam furnace which regulates both the voltage applied to the electron beam gun and the electron beam current.

Still another object is the provision of a power supply for an electron beam gun which provides a constant volt= age over the normal operating current range of the electron beam gun and which limits the maximum current supplied to the gun.

A further object of the invention is the provision of an electron beam power supply which is simple to operate, economical to manufacture, and durable in use.

In the drawings, the single figure'is a schematic circuit diagram of one embodiment of the regulated power supply.

Generally, in the illustrated power supply, the voltage supplied to an electron gun 10 in an electron furnace 12 is regulated or held constant by employing a current control device 14 as a series regulator to control the output of a high voltage DC. power supply 16. The voltage developed across the electron gun is sensed by a voltage responsive means 18 and the output thereof is supplied to a comparison means 20 which amplifies the portion of the voltage signal which is greater than a predetermined reference voltage. The current passing through the electron gun 10 is sensed by a current responsive means 22 the output of which is coupled to the comparison means 20. The comparison means amplifies the portion of the current signal which exceeds a predetermined reference voltage. The current signal and the voltage signal are adjusted so that during normal operation of the electron beam gun, the amplitude of the current signal is less than the predetermined voltage and the voltage signal is larger than the predetermined voltage. Hence, during normal operation the comparison means 20 only amplifies a signal related to the voltage signal. If the beam current signal exceeds the predetermined voltage which normally results from arcing in the electrostatic field of the electron gun, the comparison means amplifies a signal related to the current signal. During arcing, the resistance of the electron beam path is reduced thereby reducing the voltage developed across the electron gun below the predetermined reference voltage. Hence, the voltage signal during the maximum current operation is not amplified by the comparison means 20. The output signal of the comparison means 20 is applied to a control element 24 which controls the current passing through the current control device 14 in an inverse relation to the signal controlling the comparison means 20. This results in a highly regulated voltage output from zero to a maximum electron beam current. At maximum electron beam current, the current supplied to the electron beam gun is controlled so that the maximum current is not exceeded. Current control means 26 are also provided for selecting the electron beam current during normal operation of the electron beam gun and for maintaining the current at the selected amperage.

More specifically, referring to the drawings, the high voltage DC. power supply 16 may be a conventional three-phase, full wave bridge rectifier (not shown), which is connected to a source of three-phase power (not shown). The negative terminal of the DC. power supply 16 is coupled through a conductor 28 to a filament 30 of the electron beam gun 10. In this connection the conductor 28 is connected to the center tap 32 of a secondary winding 34 of a filament transformer. The filament 30 of the electron beam gun 10 is connected across the secondary winding 32. A pair of

capacitors

37 and 38 are connected between the ends of the secondary winding 34 and the center tap of the secondary winding 32. The filament is heated by connecting the primary winding 40 of the filament transformer 36 to the current control means 26, described hereinafter in greater detail.

The positive terminal of the power supply is coupled through a conductor 42 to the current control device 14 which, in the illustrated embodiment, is a hard vacuum triode having a filament 44, an anode 46 and the control element or grid 24. In this connection, the positive terminal of the DC. power supply 16 is connected to the anode 46. As illustrated, the filament 44 is heated by a filament transformer 48, the primary winding 50 of which is coupled to a source 52 of alternating current. The secondary winding 54 of the filament transformer 48 is provided with a center tap 56 and a pair of

capacitors

58 and 60 are coupled between the ends of the secondary winding 54 and the center tap 56.

As shown in the drawings, the center tap 56 of the secondary winding 54 is coupled to one end of the current responsive means 22 which, in the illustrated embodiment is a fixed resistor 62 connected in series with a rheostat 64. The other end of the current responsive means 22, as Well as the workpiece 66 in the electron beam furnace 12 and an accelerating electrode 68 of the electron beam gun 10, is grounded. Thus, the current passing through the electron beam gun 10 flows through the serially connected fixed resistor 62 and rheostat 64 and, hence, the voltage developed across the serially connected resistors 62 and 64 indicates the amplitude of the electr on beam current.

The voltage developed across the electron beam gun 10 is sensed by the voltage responsive means 18 which, in the illustrated embodiment, is a voltage divider circuit connected across the electron gun. As illustrated, the voltage divider circuit 18 includes three serially connected resistors 70, 72 and 74, the center one of which is a potentiometer. One end of the voltage divider circuit 18 is connected to the center tap 32 of filament transformer 36 of the electron gun 10 and the other end of the voltage divider circuit 18 is connected to the center tap 56 of the filament transformer 48 of the triode 14.

As illustrated, the voltage signal, which is developed between the tap of the potentiometer 72 and the center tap 56 of the triode filament transformer 48, is connected to one input of the comparison means 20. The current signal which is developed across the serially connected rheostat 64 and fixed resistors 62 is connected to a second input of the comparison means 20. The comparison means 20 compares the voltage signal and the current signal with a reference voltage and amplifies the portion of either signal which exceeds the reference voltage.

The illustrated comparison means 20 includes an or circuit 76 which includes a pair of amplifying circuits 78 and 80 having a common output and a reverse biased diode 82 in the input of each amplifying circuit. Each amplifying circuit includes a PNP transistor connected in a common emitter configuration with the reverse biased diode 82 connected between the base 84 and the input to that amplifying circuit. For one circuit this signal is the voltage signal and for the other it is the current signal. The diodes 82 are reversed biased by a constant D.C. reference voltage developed across a Zener diode 86. In this connection, the positive end of the Zener diode is coupled to the emitters 88 of the transistors 78 and 80, which are coupled together, and the negative end of the Zener diode 86 is coupled to the common connection between the voltage sensing means 18 and the current sensing means 22. A pair of reversed biased diodes 87 are connected between the base 84 and the emitter 88 of each transistor to reduce the effect of transients in the circuit.

The collectors 90 of the transistors 78 and 80 are coupled together and are biased by a constant DC. voltage. In this connection the anode of a Zener diode 92 is coupled through a pair of serially connected

resistors

94 and 96 to the common collectors 90 of the transistors 78 and 80. The cathode of the Zener diode 92 is connected to the interconnected emitters 88. Direct current voltage to break down the Zener diodes 86 and 92 is supplied by a DC. power supply 98.

The output of the or circuit 76 is amplified by an amplifying means 100 which, in the illustrated embodiment, is an NPN transistor connected in a common emitter configuration. The base 102 of the transistor 100 is connected to the junction between the serially connected

load resistors

94 and 96. The emitter 104 of the amplifier transistor 100 is connected through a pair of bias resistors 106 and 108 to the anode of the Zener diode 92. The collector 110 of the transistor 100 is biased by connecting a positive terminal of a DC. power supply 112 through a load resistor 114 to the collector. The negative terminal of the power supply 112 is connected to the common connection between the voltage sensing resistors 18 and the current sensing resistors 22. The collector 110 is also coupled to the grid 24 of the triode 14. Thus the triode 14 is positively biased "by the power supply 112 and the positive bias decreases with increases in current fiow in the amplifying transistor 100 (i.e., varies inversely). The maximum positive bias which is applied to the grid 24 is limited by a voltage limiting circuit 116 including a Zener diode 118 and a diode 120 for preventing forward current through the Zener diode 118.

The comparison circuit 20 is stabilized by connecting a pair of feed-

back capacitors

122 and 124 between the emitter 104 of the amplifying transistor 100 and the bases 84 of the or circuit transistors 78 and 80.

As previously indicated, the heating of the filament 30 of the electron gun 10 is controlled by the current control means 26. By controlling the heating of the filament 30, the electron beam current and hence the power output of the electron furnace 12, is controlled. In the illustrated embodiment, the current control means 26 maintains a signal related to the current supplied to the electron gun 10, in a predetermined relation to an adjustable reference signal. In this connection, the voltage developed across the current sensing resistors 22 is connected in series opposition to a reference voltage developed across an adjustable potentiometer 126, and this series combination of voltages is connected to a control means 128. The potentiometer 126 is connected across the voltage supply 98.

The control means 128 provides a control pulse, the width of which is related to the difference between the current voltage and the reference voltage. The control means 128 may be a conventional gate drive which includes a magnetic amplifier, the control winding of which is serially connected to the reference voltage and the current voltage. The power winding of the gate drive 128 is connected to an AC. power supply 130. The output of the gate drive 128 is employed as a gate signal for a silicon control rectifier 132 connected across a diode bridge 134. The diode bridge 134 is connected in series with the primary winding of an autotransformer 136 and the AC. power supply 130. The secondary of the autotransformer 136 is connected to the primary winding, 40 of the filament transformer 36.

In operation the desired electron beam voltage is selected by adjusting the potentiometer 72 in the voltage divider circuit 18 and the maximum electron beam current is selected by adjusting the rheostat 64. During normal operation, the current passing through the triode 14 is controlled to maintain a constant voltage across the electron gun by-the voltage developed across the voltage sensing resistor 18. When the electron beam current reaches its maximum value, the voltage across the electron gun automatically decreases to a relatively low value due to the decreased resistance of the electron path. The triode is then controlled by the voltage developed across the current sensing resistors to limit the electron beam current to its maximum value. The amperage of electron beam current during normal operation is selected by the adjusting potentiometer 126. Any variation from this adjusted current causes a related change in the voltage applied to the gate drive 128. This change in voltage, in turn, causes the output pulse from the gate drive 128 to change in width thereby causing a related change in the current flow to the filament transformer 36.

From the foregoing it can be seen that the disclosed power supply regulates the voltage developed across the electron gun so that it is at a preselected level over the normal operating range of the electron beam gun. The electron beam current is selected by adjusting a single control in the power supply and is regulated at the preselected setting. Also the power sup-ply limits the maximum current which is supplied to the electron beam gun.

Va'rious changes and modifications may be made in the above described power supply without deviating from the spirit or scope of the present invention. Various features of the present invention are set forth in the accompanying claims.

What is claimed is:

1. Apparatus for regulating the power applied to the electron gun employed in an electron beam furnace, comprising means for supplying a direct current voltage, a current control device connected in series with said voltage supply means and the electron gun, said control device having a control element for controlling the current conducted therethrough, means sensing the current flowing through the electron gun and providing a current signal in response thereto, means sensing the voltage developed across the electron gun and providing a voltage signal in response thereto, means coupled to said current sensing means and to said voltage sensing means for providing an output signal related to the electron gun voltage during normal operation of said electron gun and to the electron gun current when a predetermined electron beam current greater than normal operating current is exceeded, and means coupling the output signal to said control element for varying the current passing through said control device to maintain the electron beam voltage constant during normal operation and to limit the electron beam current to said predetermined current during arcing.

2. Apparatus for regulating the power applied to the electron gun employed in an electron beam furnace, comprising means for supplying a direct current voltage, a current control device connected in series with said volt age supply means and the electron gun, said control device having a control element for controlling the current conducted therethrough, means sensing the current flowing through the electron gun and providing a current signal in response thereto, means sensing the voltage developed across the electron gun and providing a voltage signal in response thereto, means coupled to said current sensing means and to said voltage sensing means for providing an output signal related to the electron gun voltage during normal operation of said electron gun and to the electron gun current when a predetermined electron beam current greater than normal operating current is exceeded, means coupling the output signal to said control element for varying the current passing through said control device to maintain the electron beam voltage constant during normal operation and to limit the electron beam current to the predetermined current during arcing, means coupled to said current sensing means for providing a second output signal related to variations in the current, and means coupled to said second output signal providing means for controlling the electrons supplied in the electron gun in an inverse relation to said second signal.

3. Apparatus for regulating the power applied to an electron gun employed in an electron beam furnace, comprising means for supp-lying a direct current voltage, a current control device connected in series with said voltage supply means and the electron gun, said control device having a control element for controlling the current conducted therethrough, means sensing the current flowing through the electron gun and providing a current signal related thereto, means sensing the voltage developed across the electron gun and providing a voltage signal related thereto, means for providing a reference voltage, means for comparing said reference voltage with the signal developed by said current sensing means and the signal developed by said voltage sensing means and providing an output signal related to the portion of either signal which exceeds the reference voltage, the signal developed by said current sensing means being smaller than said reference voltage during normal operation of said electron gun but larger than said reference voltage when a predetermined current greater than normal operaing current is exceeded, the signal developed by said voltage sensing means being larger than said reference voltage during normal operating of said electron gun but smaller than said reference voltage when the current exceeds said predetermined current during arcing, means comparing said reference voltage with said current signal and said voltage signal and producing a signal related to the portion of the voltage signal and current signal which is larger than the reference signal and means coupling the output signal of said comparison means to said control element for varying the cu rent passing through said control device in an inverse relation to said excess signal.

4. Apparatus for regulating the power applied to an electron gun employed in an electron beam furnace, comprising means for supplying a direct current voltage, a current control device conne ted in series with said voltage supply means and the electron gun. said control device having a control element for controlling the current conducted therethrough, means sensing the current flowing through the electron gun and providing a current signal related thereto, means sensing the voltage developed across the electron gun and providing a voltage signal related thereto, means for providing a reference voltage, means for comparing said reference voltage with the signal developed by said current sensing means and the signal developed by said voltage sensing means and providing an output signal related to the portion of either signal which exceeds the reference voltage, the signal developed by said current sensing means being smaller than said reference voltage during normal operation of said electron gun but larger than said reference voltage when a predetermined current greater than normal operating current is exceeded, the signal developed by said voltage sensing means being larger than said reference voltage during normal operation of said electron gun but smaller than said reference voltage when the current exceeds said predetermined current, means comparing said reference voltage with said current signal and said voltage signal and producing a signal related to the portion of the voltage signal and current signal which is larger than the reference signal, means coupling the output signal of said comparisonrneans to said control element for varying the current passing through said control device in an inverse relation to said excess signal, means coupled to said current sensing means for providing a second output signal related to variations in the current, and means coupled to said second output signal providing means for controlling the electrons supplied in the electron gun in an inverse relation to said second output signal.

5. Apparatus for regulating the power applied to the electron gun employed in an electron beam furnace, comprising means for supplying a direct current voltage, a current control device connected in series with said voltage supply means and the electron gun, said control device having a control element for controlling the current conducted therethrough, a current sensing resistor connected in series with the electron gun, a voltage sensing resistor connected across the electron gun, said voltage sensing resistor having a tap intermediate its ends, means coupled to said tap for providing an output signal related to the electron gun voltage during normal operation of said electron gun and coupled to the current sensing resistor for providing an output signal related to the elec tron gun current when a predetermined electron beam current greater than normal operating current is exceeded, means coupling the output signal to said control element. for varying the current passing through said control device to maintain the electron beam voltage constant during normal operation and to limit the electron beam current to the predetermined current during arcing, means coupled to said current sensing resistor for providing a second output signal related to variations in the current flow therethrough, and means coupled to said second output signal providing means for controlling the electrons supplied in the electron gun in an inverse relation to said second output signal.

6. Apparatus for regulating the power applied to an electron gun employed in an electron beam furnace, said gun having its accelerating anode connected to ground, comprising means for supplying a direct current voltage at a positive terminal and a negative terminal, the negative terminal being coupled to the filament of the electron gun, a triode having its plate connected to said positive terminal, a current sensing resistor having one end connected to the filament of the triode to provide a reference junction and the other end connected to ground, a voltage sensing resistor connected between the reference junction and the filament of the electron beam gun, said voltage sensing resistor having a tap intermediate its ends, a reference voltage supply coupled in series opposition with a first voltage developed across the voltage sensing resistor and a second voltage developed across the current sensing resistor, said second voltage being smaller than the reference voltage during normal operation of said electron gun but larger than said reference voltage when a predetermined current greater than normal operating current is exceeded, said first voltage being larger than said reference voltage during normal operation of said electron gun but smaller than said reference voltage when the current exceeds said predetermined current,

an OR circuit coupled to receive the first or second voltage which is greater than said reference voltage and providing an output signal related thereto, means coupling the output signal of the OR circuit to the grid of said triode for varying the current passing through said triode to maintain the electron beam voltage constant during normal operation and to limit the electron beam current to a predetermined current greater than normal operating current, means coupled to said current sensing resistor for providing a third output signal related to variations in the current, and means having its input coupled to said third output signal providing means and having its output signal coupled to the filament of the electron beam gun for controlling the current supplied thereto in an inverse relation to said third output signal.

7. Apparatus for regulating the power applied to an electron gun employed in an electron beam furnace, comprising first means for supplying a direct current voltage having a positive lead and a negative lead, said negative lead being connected to the filament of the electron beam gun, a triode having a plate, filament and grid, said positive lead being connected to said plate, a resistor coupling said triode filament to ground and to a work piece in the electron beam furnace, a potentiometer connected between said negative lead and a reference junction between the resistor and the filament of the triode, a first D.C. power supply means for providing a reference D.C. voltage having a negative terminal and a positive terminal which is coupled to the reference junction, a pair of PNP transistors having their emitters connected together and their collectors connected together, the nega tive terminal of said first D.C. power supply means being connected to the common emitters, a first diode coupling a base of one of the transistors to ground, a second diode coupling the tap of the potentiometer to the base of the other transistor, a second D.C. power supply means having its positive terminal connected to the negative terminal of the first D.C. power supply means, a pair of serially connected resistors coupling the negative terminal of the second D.C. power supply means to the common collectors, a NPN transistor having its base coupled to a junction between the serially connected resistors, an emitter bias resistor coupling the emitter of the NPN transistor to the negative terminal of the second D.C. power supply means, a third D.C. power supply having its negative terminal coupled to the reference junction, a load resistor coupling the positive terminal of the third D.C. power supply to the collector of the NPN transistor, the junction of the collector of the NPN transistor and the load resistor being coupled to the grid of the triode, a filament transformer coupled to the filament of the electron gun, an A.C. power supply, and a control means coupling the A.C. power supply to the filament transformer, said control means including a diode bridge rectifier in series with the A.C. power supply, a silicon controlled rectifier coupled across the bridge rectifier, a gate drive means for controlling the conduction of the silicon controlled rectifier in response to a difference in voltages applied to a control input thereof, and an adjustable fourth D.C., power supply having a positive terminal coupled to ground, said control input being coupled to the reference junction and to the negative terminal of the adjustable fourth D.C. power supply,

References Cited UNITED STATES PATENTS 2,888,633 5/1959 Carter 3239 3,072,822 1/1963 Holmes -r 315l07 3,328,672 1/1967 Park 2l9l2l ROBERT K. SCHAEFER, Primary Examiner M. GINSBURG, Assistant Examiner.

U.S. DEPARTMENT OF COMMERCE PATENT OFFICE Washington, D.C. 20231 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,400,207 September 3, 1968 Emmett R. Anderson It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shmm below:

In the heading to the printed specification, lines 5 to 7, "assignor to Temescal Metallurgical Corporation, Berkeley,

Calif. a corporation of California" should read assignor, by mesne assignments, to Air Reduction Company, Incorporated, a corporation of New York Column 6, line 48, "operating" should read operation Signed and sealed this 17th day of February 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr. E. Attesting Officer Commissioner of Patents