US3812319A

US3812319A - Automatic control of the duty cycle of an electron beam heating device

Info

Publication number: US3812319A
Application number: US00256489A
Authority: US
Inventors: I Brukovsky
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-06-10
Filing date: 1972-05-24
Publication date: 1974-05-21
Anticipated expiration: 1991-05-21

Abstract

The automatic control of the duty cycle of an electron beam heating device which controls the heating of an article includes the simultaneous measurement of the total power consumed by the electron beam heating device from its power source and the amount of energy loss in the electron gun, beam guide system and working chamber of the device. The sensed total power and energy loss are compared to determine the power consumed for the heating of an article, this power being employed as a parameter for controlling the duty cycle of the device.

Description

MTRQQ OF? 393121313 I united States Patent [1 1 [111 3,812,319 Brukovsky May 21, 1974 [54] AUTOMATIC CONTROL OF THE DUTY 3,l46,335 8/l964 Samuelson 250/495 R x CYCLE OF AN ELECTRON BEAM 3,534,386 10/1970 Mercer 219/121 EB 7 3,268,812 Meyer 6t 31. [76] Inventor: Igor Pavlovich Brukovsky, Mosfilmov ky ul k, 5 korpus 2 Primary ExammerBruce A. Reynolds b, kv 16, Mo w, U,S,$ R Assistant Examiner-Gale R. Peterson F E t Filed: y 1972 Attorney Agent or trm ric H Wa ers [21] Appl. No.: 256,489 5 A Related US. Application Data [57] ABSTR CT 3 Continuatiomimpart f Sen 83] 903 June 10 The automatic control of the duty cycle of an electron I969. I beam heating device which controls the heating of an article includes the simultaneous measurement of the total power consumed by the electron beam heating [3-0] 'Fdiign Apliricfion Pri'ofity Dita device from its power source and the amount of en- June 10, 1968 U.S.S.R ..1247754 ergy loss in the electron gun, beam guide System and V U working chamber of the device. The sensed total [5 S- 219/121 5 R power and energy loss are compared to determine, the [51] Int. Cl B23k 15/00 power consumed for the heating of an article, this Field Of Search u 121 121 power being employed as a parameter for controlling 250/495 R, 49.5 TE; 324/88, 121 the duty cycle of the device.

I 56] References Cited 2 Claims, 4 Drawing Figures UNITED STATES PATENTS 3,054,896 9/l962 Jones et 21L 250/495 R X IATENTEDMAYZI 19M 3.812.319

sum 2 or 3 FIG? AUTOMATIC CONTROL OF THE DUTY CYCLE OF AN ELECTRON BEAM HEATING DEVICE OTHER APPLICATIONS This is a continuationin-part of my earlier application, Ser. No. 831,903 filed June 10, 1969.

FIELD OF INVENTION This invention relates to electrical heating and, more particularly, to the automatic control of the duty cycle of an electronic apparatus and to electron beam heating devices.

BACKGROUND Known heating techniques have involved the automatic control of the duty cycles of electron beam heating devices. According to these known techniques, electrical parameters are controlled depending on a change of one of the parameters of the power source employed, namely: current or voltage.

Also known are electron beam heating devices which employ a vacuum space with an electron gun connected with the working chamber of the device through a beam guide system, and which include a power control unit.

A disadvantage of these known techniques and devices is that they do not provide sufficient accuracy in keeping the power level required for heating an article because the output power of the power source of the device differs from the power applied to the article to be heated by the amount of energy losses in the electron gun and electron beam guide system as well by the amount of the energy lost during the passage of the electron flow within the working chamber of the device between the beam guide system and the surface of the article being heated.

The amount of the energy loss in the electron gun usually does not exceed 0.5 to 1.5 percent of the total power of the device. However, any increase of this loss may lead to a failure of the device due to a melting of the focusing anode electrode or due to damage of the magnetic focusing lens of the beam guide system.

Also, if the pressure in the beam guide is increased to a value of SIO to 5-l0' mm. Hg, additional losses appear in the electron beam guide system which are introduced due to the interaction of the electron beam with residual gases and vapors of of the material being treated. These losses may account for 3 to 8 percent of the power consumed by the electron gun.

When the electron flow passes the section between the beam guide system and the surface of the article being heated, the loss in the working chamber of the device may come to percent of the output power of the power supply source depending on the pressure.

Because of these losses and their varying magnitudes, known devices do not provide for a high enough accuracy of control as the redistribution of the energy between the surface of the article being heated and its surroundings is not used to control the power consumed by the gun of an electron beam heating device VICC.

SUMMARY OF THE INVENTION One object of the present invention is to eliminate the above-mentioned disadvantages.

Another object of the invention is to provide an automatic control of the duty cycle of an electron beam heating device which insures a high accuracy in maintaining the power necessary for heating an article and to provide an electron beam heating device utilizing such control.

The above and other objects of the invention are achieved by providing an automatic control for the duty cycle of an electron beam heating device by which the power consumed for heating the article is separated from the total power consumed by the device, the electron beam heating device utilizing such control comprising a vacuum space in which the electron gun is connected with the working chamber of the device through an electron beam guide system, and a power control unit. According to the invention, the power control unit is provided with at least one energy loss detector mounted in the vacuum space of the device for separation of the power directly utilized for heating the article.

According to a preferred embodiment of the invention, the electron beam heating device is provided with three energy loss detectors, one of which is located within the chamber of the electron gun, the second of which is located in the beam guide system and the third of which is mounted in the working chamber of the device.

The proposed technique for the automatic control of the duty cycle of the electron beam heating device and the means for effecting the same make it possible to increase the accuracy of maintaining the power necessary for heating an article and this results in a better stabilization of the thermal distribution in the article being heated as well as in a greater reliability of the device during its operation due to the control of the power level at the electron gun electrodes and in the beam guide system.

BRIEF DESCRIPTION OF DRAWING DETAILED DESCRIPTION According to the invention, automatic control of the duty cycle of an electron beam heating device consists of the simultaneous measurement of the total power consumed by the device from its power source and the amount of the energy loss in the electron gun, beam guide system and working chamber of the device with a subsequent comparison of the measured values in order to determine the power consumed for heating the article, this power being employed as a parameter for controlling the duty cycle of the device.

The distribution of power required and consumed by an electron beam heating device is shown in FIG. ii.

A. is the power fed by a supply source to the device; B is the power required to heat the article and C is the power lost inside the vacuum chamber of a conventional electron beam heating device along the path of the electrons from the cathode surface of the electron gun of the device to the metal surface of the article being heated. The power lost (value C) is composed of energy lost in the working chamber K of the apparatus and in the beam guide system L due to the interaction of the electron flux with the molecules of the residual gases and vapors of the material being treated, and also the energy lost in the electron gun and in the beam guide system (value M) due to the collecting of a part of the electron flux on the elements of the apparatus (such as, for example, on the anode of the electron gun or the magnetic focusing coil).

Basically the present invention resides in an apparatus which:

a. measures the value of power lost in the vacuum chamber of the apparatus (value C) by measuring the various kinds of power lost in various sections of the vacuum chamber (values K, L and M) in accordance with any of several parameters (pressure, temperature of structural elements, etc.) with detectors;

b. compares the energy lost (value C) with the power of the apparatus supply source (value A) which is measured by a detector and provides through comparison or substraction the value of power spent directly on heating the article (value B) to generate a signal proportional to this value for automatically controlling the electrical operating duty cycle of the apparatus;

0. compares the signal proportional to the power consumed in heating the article (value C) with the reference signal proportional to the rated power required to heat the article and supplies a difference signal to the cathode supply control unit to control cathode heating in order to maintain the power consumed in heating the article at a given level, and in an emergency generates a signal to cut off the apparatus from the source of power.

Temperature and/or pressure can be employed in detecting the various energy losses. The relationship between total power of the apparatus and the temperature and pressure at difierent points of the apparatus can be illustrated as follows:

It is well known that, as the electron flux passes through an anode opening, some of the electrons are retained by the anode and are prevented from reaching the surface of the article being heated. The electric current generated by these electrons flows through the anode, heating it and consuming a part of the power of the supply source (value A).

A signal transmitted by a detector (which, depending on the specific design of the apparatus, measures either the anode temperature of the value of current flowing through the anode insulated from ground and indicating the extent of anode heating) can be amplified and used for comparison with the power of the supply source. This makes it possible to adjust the electrical operating mode of the apparatus through the cathode of the heating device depending on the power required to heat the articles (value B) regardless of the power lost in the anode (value K).

As the pressure in the working chamber rises due to nonuniform gas release from the article being heated,

energy losses due to ionization of the molecules of residual gases and metal vapors with the electron flux in the working chamber can be as high as 20-25 percent.

When the pressure rises above a predetermined level, a signal from a detector is directed to a power control unit and, after operations identical to those described above, enables the electrical operating mode of the apparatus to be controlled depending on the power directly required to heat the article (value B) regardless of the power lost to ionization in the working chamber of the apparatus (value M).

As more specifically shown in the FIG. 2, an electron beam heating device 1, comprising in its vacuum space an electron gun 2, a beam guide system 3 and a working chamber 4, is supplied power by a power supply source 5. The cathode of the electron gun 2 is supplied by a separate cathode power supply source 6.

A power control unit 7 is electrically connected with the output of the power supply source 5 of the device through a total power detector 8. Energy loss detectors or sensing elements 9, it) and iii are mounted in the chamber of the electron gun 2, in the beam guide system 3 and in the working chamber 41 of the device 1, respectively, and are connected with the corresponding inputs of the power control unit 7 through the amplifiers l2, l3 and M respectively.

Signals are fed from the detector 9 through the amplifier l2, from the detector 10 through the amplifier l3 and from the detector ll through the amplifier 14 to inputs of the power control unit 7, another input of which is continuously supplied with a signal from the detector 8 whose signal is proportional to the total power supplied to the device other than that supplied by source 6 to the gun cathode.

The signals from the detector 8 and the signals from the detectors 9, l0 and Ill are fed simultaneously or from one or more of these detectors are compared in the power control unit 7 for the separation or formation of signals proportional to the power utilized from heating an article. From the output of the power control unit 7, the thusly generated signals are fed to the cathode power supply source 6 for controlling the duty cycle of the device l. in emergency conditions these signals are fed to the power supply source 5 for deenergizing the electron beam heating device.

The amplifiers l2, l3 and 14 make it possible to control the operation of the device 11 by taking into account various effects of the absolute value of the signals of the detectors upon the duty cycle and output power of the device ll. This allows employing detectors of different types simultaneously. For example, the detectors 9, l0 and ill in the form of pressure transmitters, temperature sensing elements and probes insulated from ground may be used.

From the above, it is clear that a signal proportional to the total power supplied to the device is fed to the input of the power control unit 7 from the detector 8. The detectors or sensing elements 9, l0 and 11 arranged at difierent points in the device are adapted to measure energy losses of the electron beam in the electron gun, in the beam path control system and in the working chamber of the device, caused by the deposition of a portion of the electron flux on the structural element of the device and by energy dissipation in metal vapors and residual gases. The determination of the value of these energy losses is effected by use of the sensing elements 9, l0 and 11 which provide for indirect indicative values, such as electron deposition current on the structural elements of the device, or temperature and pressure within volume all according to well known conventional sensing techniques.

The detector or sensing element 9 arranged within the chamber of the electron gun 2 is adapted to indicate energy losses in the chamber of the electron gun 2. Depending on the specific design features of the electron gun employed in the device, of main importance for insuring its reliable operation and, hence, for accurately maintaining the power utilized for heating the article involved, there may be either the energy evolving at the anode of the electron gun, or the energy evolving in the interelectrode space. At a certain value of power losses in the electron flux at the anode, the latter may fail due to melting, which will cause failure of the device and trouble in the performance of the technological cycle. Should there be an increase in the power output in the interelectrode space due to a pressure rise in the gun chamber, the electrical strength of said space will drop because of ionization of vapor molecules and residual gases, and this may lead to a breakdown between the electrodes, emergency disconnection of the device and irrepairable damage incurred to the article treated.

The signal from the sensing element or detector 9 coming through the amplifier 12 to the power control unit 7 of the device makes it possible to prevent such emergencies and thus enhance the accuracy and efficiency of maintaining the power evolving in an article being heated.

The signals from the sensing elements or detectors 9, l0 and 11, proportional to the energy losses in different points of the device, through the corresponding

amplifiers

12, 13 and 14, come to the power control unit 7 of the device, the characteristic of the amplifiers being chosen in accordance with the types of the sensing elements employed and remaining invariable in the process of the devices operation. Simultaneously, to the power control unit from the sensing element or detector 8, there comes a signal proportional to the total power of the device. The power control unit 7 functions as an adder and/or substractor which separates from the value proportional to the total power, with due regard for the signals arriving from the sensing elements 9, l0 and 11, a value a value that is proportional to the power utilized directly for heating the article involved, the latter value being used for controlling the operation duty cycle of the device.

The total power of the device differs from the amount of power utilized directly for heating the article involved by the value of power losses in the electron gun chamber, in the beam path control (beam guide) system and in the working chamber of the device. The invention thus utilizes means for separating the power employed directly to heat articles from the total power consumed by the device and handling these indirect process parameters which characterize the amounts of power losses taking place in different zones of the device. The thus separated signal, which is proportional to the power directly utilized for heating the articles being treated, is used for the automatic control of the device duty cycle.

The terms duty or duty cycle" are used herein to denote electrical parameter or parameters by which the devices operation can be controlled.

Additionally, it will be noted that the detector does not actually sense the total power consumed by the device since it takes no account of the power consumed by the source of power of cathode 6 nor of the power consumed by the vacuum pumps and auxiliary mechanisms. The power sensed by detector 8 (value A, FIG. 1) would be more precisely described as the power supplied the device by power source 5 or the power supplied power source 5 from the mains, but the term total power is used for the sake of simplicity.

FIG. 3 is partly schematic and partly block diagram of power control unit 7. It will be clear that the output voltages of

amplifiers

12, 13 and 14 which are proportional to the energy lost in the working chamber (K) of the device, the beam guide system (L), and the electron gun (M) are fed, respectively, to resistors 15, 16 and 17, their polarities being as shown. A voltage proportional to the power (A) supplied by the power source from the power detector is fed to resistor 18, its polarity being as shown. From reference voltage source 25 comprised in unit 7, resistor 19 receives a voltage which is proportional to the-rated power released in the article being heated, the polarity of said voltage also being as shown.

The difference between the voltage at resistor 18 and the total voltage drop over resistors 15, 16 and 17 is proportional to the power released at a given moment in the article being heated (value B, FIG. 1).

The voltage at

output terminals

20 and 21 of unit 7 which is proportional to the difference between value B and the rated value is used to change the heating conditions of the electron gun cathode by using unit 6 in such a manner as to reduce said difference to zero.

In parallel connection with resistors 15, 16 and 17 are the inputs of

threshold elements

22, 23 and 24 which are formed of maximum voltage relays. When output voltages at

amplifiers

12, 13 and 14 exceed the actuation level of any of

threshold elements

22, 23 or 24, a signal is generated at the output of the respective threshold element whereby unit 5'is cut off from the device. The rated actuation levels of the threshold elements are equal to the maximum permissible values of K, L and M.

As seen in FIG. 4, electron beam heating device 1 is comprised of electron gun chamber 2, a chamber of beam guide system 3 and chamber 4 whose vacuum vessels are communicating. Electron gun chamber 2 and beam guide system 3 are evacuated by

vacuum pumps

26 and 27, respectively, while working chamber 4 is evacuated by vacuum pump 28.

The electron gun is comprised of focusing electrode 30 and anode 31 disposed in the vacuum vessel chamber 2 which also accommodates magnetic focusing system 32.

The electron beam is focused in beam guide chamber 3 by means of magnetic focusing

systems

33 and 34. Article 35 which is being heated is accommodated in working chamber 4.

Electron gun cathode 29 is energized by power source 6 which is comprised of matching transformer 36, opposing-parallel thyristors 37 and 38 and thyristor control unit 39. Unit 39 which controls thyristors 37 and 38 in a vertical phase mode is similar in design to that described in Semiconductor Controlled Rectifiers" by F. Gentry, F. Gutzewiller, N. Holonyak, E. von astrswr flswy rls.NYY-Z 9 The electron gun is energized by power source which is comprised of rectifier 40, matching transformer 41, cutout switch 42 and ON-OFF control unit 43. The design of the ON-OFF control unit is familiar to those skilled in the operation of commutation equipment.

Energy detectors 9, l0 and 11 are accommodated, respectively, in the vacuum vessels of the chambers of electron gun 2, of beam guide system 3 and in working chamber 4. Depending on the specific design of electron beam heating device 1 they may be disposed in three, two or any one of the chambers.

The function of energy loss detectors 9, l0 and ll may be performed, depending on the specific design of the apparatus, by temperature detectors 44, 45 and 46, by probe units 47, 48 and 49 insulated from the housings of the respective chambers or by pressure detectors, 50, 51 and 52.

Chambers

2, 3 and 4 or any of them may accommodate several detectors of a variety of designs. Thus, working chamber 4 may accommodate detectors 46, 49 and 52 at the same time. Any one of these may be selected for use as energy loss detector ll by means of control switch 55. Control switches 53 and 54 serve a similar purpose.

The function of temperature detectors 44, 45 and 46 may be fulfilled by thermocouples or optical photoelectric pyrometers, a description of whose designs may be found in any popular handbood on temperature measurement technology.

The design of detectors 47, 48 and 49, for example, have been described in Plasma Diagnostics edited by W. Lochte-Holtgreven, Kill, University, North Holland Publishing Company, Amsterdam, 1968.

The function of pressure detectors 50, 51 and 52 may be fulfilled by ionization or electric discharge pressure gauges described in Pressure Measurement in Vacuum Systems by J.H. Leck, London, EC 4, 1964, and other publications.

What is claimed is:

1. An electron beam heating device operating with a power supply and provided with an automatically controlled heating operation, said device comprising in combination: means providing a vacuum space, an electron gun accommodated within said vacuum space, a beam guide system accommodated within said vacuum space and operatively associated with said electron gun, a working chamber device in said vacuum space and operatively associated with said electron gun through said beam guide system, three energy loss detectors accommodated within said vacuum space for separately sensing power lost during heating of an article in said working chamber, and a control unit connected with said energy loss detectors and power supply and adapted for controlling said heating operation, one of said detectors being mounted adjacent the electron gun, a second of said detectors being mounted in the beam guide system and a third of said detectors being mounted in the working chamber.

2. A device as claimed in claim 1 wherein said gun includes a cathode, said device comprising a power supply for heating said cathode, said control unit being coupled to and controlling the latter said supply.