US3637970A

US3637970A - Induction heating apparatus

Info

Publication number: US3637970A
Application number: US52186A
Authority: US
Inventors: Ronald J Cunningham
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-07-06
Filing date: 1970-07-06
Publication date: 1972-01-25
Anticipated expiration: 1989-01-25

Abstract

A circuit for supplying a series of current pulses to an output coil, such as a coil used for induction heating, can be constructed utilizing a timing circuit adapted to be connected to a DC power supply and a resonant circuit including the output coil connected to the timing circuit. The timing circuit used includes a current discharge or release means such as an SCR (silicon-controlled rectifier) and a trigger means such as a trigger diode (bidirectional diode thyristor) for actuating or firing the release means in response to current supplied by the power supply so that the release means will supply current to the resonant circuit. The current supplied to the resonant circuit results in the development of a resonant current in opposition to the supplied current. Such resonant current feeds back to the timing circuit so as to render the release means no longer operative to supply current to the resonant circuit until such time as thereafter the trigger means, as a result of power supplied to it from the power supply, actuates the release means so that it will again supply current to the resonant circuit.

Description

United States Patent Cunningham [4 1 Jan. 25, 1972 154] INDUCTION HEATING APPARATUS [57] ABSTRACT [72] Inventor: Ronald .I. Cunningham, 4360 Eagle Rock A circuit for supplying a series of current pulses to an output View Drive, Los Angeles, Calif. 90041 coil, such as a coil used for induction heating, can be constructed utilizing a timing circuit adapted to be connected to a [22] Flled: July 1970 DC power supply and a resonant circuit including the output 2 APPL N 52,13 coil connected to the timing circuit. The timing circuit used includes a current discharge or release means such as an SCR (silicon-controlled rectifier) and a trigger means such as a [52] 219/10-75, 307/318 trigger diode (bidirectional diode thyristor) for actuating or [51] Int. Cl. ..H05b 5/00 fi i the release means in response to current Supplied by he [58] Field of Search ..219/10.75;307/117, 129, 271, Power Supply so that the release means will Supply current to 307/3 1 3 the resonant circuit. The current supplied to the resonant circuit results in the development of a resonant current in op- [56] Rem'enccs clued position to the supplied current. Such resonant current feeds back to the timing circuit so as to render the release means no UNITED STATES PATENTS longer operative to supply current to the resonant circuit until 3,466,528 9/1969 Adams ..321/45 such time as thereafter the gg r m n as a resul f power 3,475,674 10/1969 Port fi ld t 1 ,321/45 supplied to it from the power supply, actuates the release 3,339,126 8/1967 Horowitz ..317/ 124 means so h i will gain supply curren to the resonant cir- 3,332,036 7/1967 Kappenhagen et al. ..331/l73 cuit 3,021,413 2/1962 Blok ..219/10.75 3,187,204 6/1965 13 Claims, 7 Drawmg Figures Adkins ..307/1 17 Primary Examiner-J. V. Truhe Assistant Examiner-Gale R. Peterson Attorney-Edward D. OBrian INDUCTION HEATING APPARATUS BACKGROUND OF THE INVENTION The term induction heating is commonly used to designate heating processes in which an object or charge of or containing one or more metals is heated by subjecting such an object or charge to an alternating magnetic flux. Such a flux serves to induce rapidly reversing currents or eddy currents in whatever is being heated by this type of process so as to result in the generation of heat. Conventionally such an alternating magnetic flux is generated by passing an alternating current through a coil surrounding the object or charge being heated. Frequently, such a coil has to be cooled as by circulating water through it to avoid the coil being melted.

The alternating currents used in this type of heating are normally generated utilizing conventional equipment for generating alternating currents of the particular frequencies to be employed. In practice the frequencies normally used vary in the range of from about 400 to about 500,000 cycles per second. The precise frequency chosen for any specific induction heating application will depend upon the nature of that application. In general higher frequencies within the range indicated are employed where it is desired to obtain essentially a surface type heating. Thus, in so-called electronic or high-frequency induction heating designed to heat primarily the outer surface or region of a metal object frequencies of from 100,000 to 500,000 cycles per second or even higher are utilized.

An understanding of the present invention is not considered to require a detailed understanding of all of the problems which have been encountered with conventional induction heating processes as are briefly indicated in the preceding discussion. Frequently conventional induction heating involves the use of radio frequencies. This entails or results in various problems which are familiar in the electronics industry. With conventional induction heating processes power transmission problems have frequently made it necessary or advisable to utilize special transmission cables and have frequently resulted in significant power losses. Also with conventional induction heating processes both highand lowfrequency components of an applied alternating current have been equal, making it impossible to obtain simultaneously heating effects at different depths within an object or charge being heated.

SUMMARY OF THE INVENTION An objective of the present invention is to provide new and improved induction heating. More specifically an objective of the present invention is to provide relatively simple, relatively inexpensive, relatively efiective circuits for use in induction heating. A further objective of the invention is to supply circuits which provide unique current pulses to an output coil, such as a coil used for induction heating, which pulses are especially useful in induction heating.

It is not to be assumed from these objectives that such circuits are only useful in induction heating. They can be employed in other applications where ever it is desired to supply a series of timed current pulses to an output coil. Another objective of the present invention is to provide a new process for induction heating utilizing what may be regarded as both high and low frequency components so as to simultaneously obtain heating effects at different depths within an object or charge being heated.

In accordance with this invention these and various related objectives are achieved through the utilization of a circuit for supplying a series of current pulses to an output coil such as the coil used for induction heating. Such a circuit in accordance with this invention includes a timing circuit adapted to be connected to a DC power supply and a resonant circuit including the outp u t coil connected to the timing circuit. The timing circuit employed includes a current discharge or release means such as an 'SCR (silicon-controlled rectifier) and a trigger means such as a trigger diode (bidirectional diode thyristor) and actuating the current release means so as to supply current to the resonant circuit.

In a circuit of this invention the current supplied to the resonant circuit results in the development of a resonant current in opposition to the supplied current which feeds back to the release means so as to render the release means no longer operative to discharge current to the resonant circuit until thereafter the trigger means, as a result of the power supplied to it from the power supply, actuates the release means so that it will a again supply current to the resonant circuit.

With the circuit of this invention the rate at which pulses are supplied to the output coil in the resonant circuit can be varied and the shapes of such pulses can be varied to a limited extent as may be desired for various specific applications. With a circuit in accordance with this invention the current pulses supplied to the output'coil used have a waveform including positive and negative: components of different magnitudes. Pulses with such waveforms are considered quite advantageous in enabling circuits of the invention to be used in induction heating to heat an object or charge at different depths.

BRIEF DESCRIPTION OF THE DRAWINGS Further details of the present invention as well as the manner in which the invention achieves the aforegoing objects and other objectives and advantages of the invention will be apparent from a detailed consideration of the remainder of this specification, the appended claims and the accompanying drawings in which:

FIG. 1 is a schematic wiring diagram of a presently preferred embodiment or form of a circuit in accordance with this invention;

FIGS. 2 to 5 are curves showing current pulse waveform shapes at various points in the circuit shown in FIG. 1 during the operation of this circuit;

FIG. 6 shows a modification of the circuit shown in FIG. 1 so as to utilize a feedback means in order to govern or control the pulse repetition rate of pulses generated in an output coil used in a circuit of the type shown in FIG. 1;

FIG. 7 is a modified schematic wiring diagram of a modified embodiment or form of a circuit in accordance with this invention. i

From a detailed consideration of the drawings and of the remainder of this specification it will be realized that the various circuits shown embody the concepts of the present invention, but are not in a technical sense the invention itself. The basic concepts or principles of the present invention can be embodied within other somewhat different circuits through the use of routine electronic design skill.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawings there is shown a presently preferred form or embodiment of a circuit 10 of this invention which is primarily intended for use in induction heating, but which can be used for other purposes. This circuit 10 can be considered as being composed of two subcircuits, a timing circuit I2 and a resonant circuit 14. A significant feature of this invention is the simplicity of these subcircuits.

The timing circuit 12 is composed of an SCR (silicon-controlled rectifier) 16, a trigger diode (bidirectional diode thyristor) a break-back semiconductor) 18, a capacitor 20 and a variable resistor 22. These components are connected by means of wires 24 so that both one terminal of the resistor 22 and the base of the SCR 16 can receive 8+ power from an appropriate power source (not shown) through an input wire 26, so that the other terminal of the resistor 22 is connected to one side of the capacitor 20 and to one side of the trigger diode 18, so that the other side of this diode 18 is connected to the gate of the SCR l6 and so that the other side of the capacitor 20 is connected to the cathode of the SCR 16.

The power source used may be any convenient DC power source. If desired power may be supplied to the input wire 26 through a mechanical or electronic timing means used to determine the period of operation of the circuit 10. The particular wire 24 connecting the capacitor 20 and the cathode of the SCR [6 is connected to a connecting wire 28 used to supply power from the timing circuit 12 to the resonant circuit 14.

This resonant circuit 14 is a tank-type LC resonant circuit including a comparatively large inductance coil 30, a capacitor 32, and a work coil 34 of significantly less inductance .than the coil 30. These components in the circuit 14 are connected by wires 36 between the connecting wire 28 and a ground wire or connection 38 so that the inductance coil 30 forms one leg of the circuit 14 and so that the capacitor 32 and the work coil 34 are connected in series so as to constitute the other leg of this circuit 14. Preferably this circuit 14 is constructed so as to include terminals 40 useful in connecting the work coil 34 into the circuit at a significant distance from the other components of this circuit 14.

When the circuit is to be used DC power is supplied through the wire 26 to both the resistor 22 and the anode of the SCR [6. At the moment of initial use of this circuit 10 this SCR 16 will be in a nonconductive state or condition and so will not pass the applied current. The applied current will, however, pass through the resistor 22 to both the capacitor 20 and the diode 18. The resistor 22 serves a significant function as current is applied in protecting the diode 18 from the direct application of 8+ current since if such current were applied directly to the diode 18 it would automatically go to its conductive state or condition.

As current reaches the capacitor 20 it will become charged,

but the diode 18 will not pass the current applied to it until the capacitor 20 is charged to what is referred to as the breakback voltage of this diode 18. When the capacitor 20 is charged, to this point, the diode 18 will go into what may be considered as a conductive state and will allow current to pass to the gate of the SCR 16. As the diode 18 goes into this conductive state it will continue to allow current to pass at a lessor voltage than was required to render it conductive, and the capacitor 20 will be discharged through the diode 18 to the gate of the SCR 16.

The .current which passes to the gate of the SCR 16 will render the SCR I6 conductive so that it releases" or discharges" or passes" the applied B+ current from its anode to its cathode. The current released by the SCR 16 as a result of this will flow to the resonant circuit l4 through the wire 24 attached to the base of the SCR l6 and the wire 28. Because of the function of the assembly of the resistor 22, the trigger diode l8 and the capacitor 20, as connected together they may be regarded as a trigger circuit" 42 for causing the release of current through or by the SCR l6 and may be termed a trigger means for this purpose. Because of the function of the SCR 16 it may be considered as a release means for releasing or passing current applied to it in response to a signal from the trigger circuit 42.

The current passed by the SCR l6 reaching the resonant circuit 14 will flow in what may be regarded as an expected manner. Because of the inductance of the coil the capacitor 32 will be charged as current is released to the resonant circuit 14, and charging current will pass through the work coil 34. This resonant circuit 14 will resonate in response to the applied current so as to give rise to a resonant current in opposition to the B+ current released to or supplied to the resonant circuit 14. The resonant current created in this manner will flow back to the timing circuit 12 through the wire 28 and the wire 24 connected to the cathode of the SCR 16. When the resonant current moving in this manner approximates the applied B+ voltage it will act in opposition to the current flowing through the diode l8 and flowing through the SCR 16 so as to cause the diode 18 to no longer pass a current to the SCR l6 and so as to render the SCR l6 nonconductive. By this it is meant that the resonant current created as described will result in no more B+ current being supplied to the resonant circuit 14 through the SCR 16.

At this point in time the circuit 10 will perform as when power is initially supplied to the timing circuit 12. In other words the capacitor 20 will become charged to the break-back voltage of the diode l8, and then this diode 18 will allow current to pass to the gate of the SCR 16. This will result in another pulse of current passing to the timing circuit 14. As this occurs a further pulse of current will flow across the work coil 34 and a pulse of resonant current will be developed which will again prevent the applied B+ current flowing to the resonant circuit 14. The whole cycle of operation will continue again. The rate at which these operation cycles continue can be varied by adjusting the variable resistor 22. However it is noted that this rate is limited by the speed at which the SCR 16 can be switched between conductive and nonconductive states to below what is normally considered a radio frequency range.

A satisfactory circuit as shown in FIG.-l can be constructed for use with a 8+ power supply of from 5 to 100 volts by using the following components: resistor 22-l 0 to 250 K/ohms, SCRl6General Electric SCR C141; capacitor 32-20 MFD, coil 30-20MH; work coil 34-15-25 micro H. When the circuit 10 is constructed with such components the pulses of current passing in the circuit will have various wave forms as indicated in FIGS. 2-5 of the drawings during each cycle of operation. At the point A, the current used to charge the capacitor 20 and which flows through the diode 18 will have a wave shape as indicated in FIG. 2. At the other side of this capacitor 20 where this capacitor 20 is connected to the resonant circuit 14 at point B the current wave shape will be as shown in FIG. 3. The wave shape of the current at the capacitor 32 at point C is shown in FIG. 4. Most important, however, the waveform of the pulses across the work coil 34 as shown in point D in FIG. I are shown in FIG. 5 of the drawings.

This shape of a current pulse as developed across the work coil 34 as shown in FIG. 5 is considered quite important to this present invention. It will be noted that a current pulse as shown has both positive and negative components of different magnitudes. The difference in the amplitude of these two components is considered to give rise to different heating effects at different depths in a charge or object being heated by the work coil 34 when the circuit 10 is used for induction heating. For certain applications this is advantageous. This is to be contrasted with prior induction heating processes in which the positive and negative values of the current pulses applied to a work coil used in induction heating have been equal or nearly equal. Such prior processes have been of such a nature that they have tended to heat to or at substantially a single depth.

The invention is also significantly advantageous for use in induction heating because the circuit 10 can be used employing a work coil 34 of virtually any desired shape. This work coil 34 may be standard cylindrical coil. It may also be a flat spiral like coil. It may also be such a spiral like coil bent in a U or other analogous shape so as to fit around a part of an object being heated. Because of the fact that the coil 34 may have many different shapes, the circuit 10 is especially advantageous for use with many induction heating applications where in the past induction heating could not be satisfactorily employed.

The circuit 10 is also considered quite advantageous because of the fact that it does not use radio frequencies. Thus, when the circuit 10 is used for induction heating problems such as radio frequency burns encountered with prior related induction heating apparatus are not encountered. Because of the nature of the current pulse applied to the work coil 34, these pulses can be easily transmitted across significant distances without significant power losses. This is frequently considered quite beneficial and advantageous.

In FIG. 6 of the drawings there is shown a modified circuit of the present invention which is essentially very similar to the circuit 10 shown in FIG. 1. In the interest of brevity various parts of the circuit 100 which are the same or substantially the same as corresponding parts of the circuit 10 are not separately described herein and are indicated in the drawings and where necessary for explanatory purposes in the specification by the numbers previously used to indicate such parts preceded by the number 1.

The circuit 100 utilizes a feedback circuit or means 50 in order to accurately control the frequency of the current pulses across the work coil 134.ln order to accomplish this, it employs a coil 52 which is coupled magnetically to the coil 130 by what may be termed as transformer-type coupling. Wires 54 are employed to connect the ends of a potentiometer 56 across the ends of the coil 52. Other wires 58 connect a lightbulb 60 between one end of the coil 52 and the wiper on the potentiometer 56. With this circuit 50 the lightbulb 60 is located opposite a conventional light-sensitive resistor 122 used to replace the variable resistor 22 in the circuit 10.

The operation of the circuit 100 is essentially very similar to the operation of the circuit 10. The timing circuit 112 and resonant circuit 114 in the circuit 100 operate as in the circuit 10. When, however, pulses of current pass through the coil 130, these induce a voltage in the coil 52. The induced voltage in the coil 52 is used so as to cause illumination of the lightbulb 60 in accordance with the frequency of the pulses flowing in the resonant circuit 14. Variations in the illumination of the lightbulb 60 in turn effect the resistance value of the resistor 122 and this in turn results in a variation in the pulse repetition rate at which current is passed by the SCR 116 as when the variable-resistor 22 is adjusted in the circuit 10.

With this circuit 100 asthe frequency applied to the work coil 134 decreases, the voltage in the coupled coil 52 increases so as to increase the intensity of light from the lightbulb 60. Such increase in the intensity of the light from the lightbulb 60 will serve to decrease the resistance of the resistor 122, resulting in an increase in the pulse repetition rate or frequency applied to the work coil 134. This in turn will result in a decrease in the intensity of the light by the bulb 60 as the result of a manner of operation as indicated.

In FIG. 7 of the drawings there is shown a still further modified circuit 200 of the present invention which in effect is two of the circuits 10 as shown in FIG. 1. In the interest of brevity, various parts of the circuit 200 which are the same or substantially the same as corresponding parts of the circuit 10 are not separately described herein and are indicated in the drawings and where necessary for explanatory purposes, in this specification by the numbers previously used to indicate such parts preceded by the number 2.

In the circuit 100 the timing circuit 212 indicated at the right of FIG. 7 of the drawings is identical with the timing circuit 12 previously indicated except for the fact the a wire 224 connected to the variable resistor 222 is connected to the wire 228 instead of being connected directly to a source of 8+ power. In this timing circuit 212 shown at the right of FIG. 7 the base of the SCR 216 is connected to the wire 226 which is used to lead to a source of 3+ power.

Both of the timing circuits 212 shown in FIG. 7 of the drawings in the circuit 200 operate in the same manner as the timing circuit 12 previously described with one difference. The timing circuit 212 as shown at the right hand side of FIG. 7 includes a trigger circuit 242 which is charged so as to permit the associated SCR 216 to pass B+ current by current pulses passed by the SCR 16 in the timing circuit 202 at the left of FIG. 7. This will result in the sequential operation of the two timing circuits 212, the second or right hand circuit being operated in response to operation of the first timing circuit 212. With this structure this will result in the work coil 234 at the left of FIG. 7 receiving a current pulse as for induction heating and then the work coil 234 at the right of FIG. 7 receiving a current pulse for the same purpose at a subsequent period.

The circuit 200 is normally used with the two work coils 234 in close proximity or intertwined with one another. It is useful in avoiding magnetization effects in an object or charge being heated by induction heating. The circuit 200 is also considered advantageous inasmuch as it applies relatively frequent current pulses through the two work coils 234 in induction heating. In general, the more rapid the pulse repetition is in such heating the more rapidly an object or charge is heated.

From a careful consideration of the preceding it will be realized that many variations may be made in the precise circuits shown through the use or application of routine electronic skill. Thus, for example, different feedback means than the precise feedback circuit described may be employed. Various circuits as indicated may be operated in parallel where this is desired. In all these circuits as herein indicated, the components used must be optimized with respect to one another to achieve a pulse repetition rate as desired for a particular application. It will be realized that different rates will be desired for various different applications to which circuits as described may be put.

I claim:

1. A circuit for supplying a series of timed current pulses to a work coil which comprises:

a timing circuit means for receiving a DC current from a power source and for supplying current pulses of such power,

said timing circuit means including release means for releasing current from said power source and trigger means for causing the release of current by said release means in response to power from said power source,

said trigger means being connected to said release means,

said release means and said trigger means both being connected to said power source,

said release means being responsive to a current supplied to it in opposition to a current released through it from said power source so as to no longer release current from said power source,

a resonant circuit means for receiving current released by said release means connected to said release means so as to receive such current, said work coil forming a part of said resonant circuit means,

said resonant circuit means being capable of developing a resonant current in opposition to the current released to it by said release means, which resonant current will be fed back to said release means to cause said release means to no longer current to said resonant circuit means until said trigger means again actuates said release means.

2. A circuit as claimed in claim 1 wherein:

said release means is a silicon-controlled rectifier.

3. A circuit as claimed in claim I wherein:

said trigger means is a trigger circuit including a resistor, a capacitor and a trigger diode, said resistor, said capacitor and said diode being connected so that said capacitor is charged by current from said power source which has passed through said resistor to a sufficient extent to cause said diode to become conductive, said diode being connected to said release means so as to cause actuation of said release means when said diode becomes conductive and passes a current.

4. A circuit as claimed in claim 1 wherein:

said resonant circuit is an LC tank circuit having inductance of one leg thereof and having a capacitance and said work coil in the other leg thereof.

5. A circuit as claimed in claim I wherein:

said release means is a silicon-controlled rectifier,

said trigger means is a trigger circuit including a resistor, a capacitor and a trigger diode, said capacitor and said diode being connected so that said capacitor is charged by current from said power source which has passed through said resistor to a sufficient extent to cause said diode to become conductive, said diode also being connected to the gate of said silicon-controlled rectifier so as to pass a current to said silicon controlled rectifier when said diode becomes conductive,

the base of said silicon-controlled rectifier is adapted to be connected to said power source,

the cathode of said silicon-controlled rectifier and said capacitor are connected to said resonant circuit means,

said resonant circuit means is an LC tank circuit having an inductance in one leg thereof and having a capacitance and said work coil in the other leg thereof.

6. A circuit as claimed in claim 5 wherein:

8. A circuit as claimed in claim 7 including: a photosensitive resistor connected to said trigger means so that power to said trigger means passes through said resistor and wherein,

said feedback means includes means for receiving power from said resonant circuit means coupled to said resonant circuit means and an illumination source operated thereby, said illumination source being located so that the illumination therefrom controls the resistance of said resistor.

9. A circuit as claimed in claim 1 including:

a second of said timing circuit means and a second of said resonant circuit means connected thereto,. said second resonant circuit means including another work coil,

said trigger means of said second timing circuit means being connected to said release means of the first-mentioned timing circuit means so as to be actuated thereby, allowing the release means of the second timing circuit means to release a current in response to current released by said release means of said first-mentioned timing circuit means.

10. In an apparatus for induction heating in which a current from a power supply is passed to a work coil through intermediate circuitry the improvement which comprises:

said intermediate circuitry consisting essentially of a timing circuit means and a resonant circuit means, said timing circuit means being connected to said power supply and to said resonant circuit means so that power is supplied to said resonant circuit means through said timing circuit means, said resonant circuit means including said work coil as a part thereof,

said timing circuit means being capable of releasing a current to saidresonant circuit means,

said resonant circuit means being capable of resonating in response to current released to it through said timing circuit means so as to develop a resonant current in opposition to the current supplied to it through said timing circuit means,

said timing circuit means being responsive to the resonant current developed in said resonant circuit means so as to no longer supply a current to said resonant circuit means until said timing circuit means is actuated so as to release current to said resonant circuit means because of power supplied to it from said power supply.

11. A process of induction heating in which current from a power supply is used to supply power to a work coil in which the improvement comprises:

using said power supply to supply current to actuate a discharge means so that it will pass the current supplied to it to a resonant circuit including said work coil, causing said resonant circuit to develop a resonant current in opposition to the current passed by said discharge means and thereafter using said resonant current to render said discharge means incapable of passing a current from said power supply until said discharge means is again actuated by current supplied by said power supply and automatically repeating the steps herein specified at intervals as determined by the circuit components employed.

12. A process as claimed in claim 13 wherein:

said discharge means is a silicon-controlled rectifier and said discharge means is actuated by a trigger means connected to said silicon-controlled rectifier and to said power supply, said trigger means also being connected to said resonant circuit.

13. A process as claimed in claim 11 wherein:

said current pulses have a wave shape as indicated in FIG. 5

of the drawings.

and that said Letters Patent are hereby cortected as shown below:

' 222%? I UNITED STATES ,PATENT OFFICE v I CERTIFICATE OF CORRECTION Pat ent NQ'. 3,;637 .970 ed January 25., 1972 ve VRONALD J CUNNINGHAM It is certified that error appears in the above-identified patent In the claims, claim 12 should be dependent on Claim 11 t Signed and seeled this 10th day of October 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 2 22 3 UNITED STATES PATENT OFFICE RTIFICATE 0F CORREQTON Patent No. 3 ,637 ,970 Dated January 25, l972 Inventor( LD J. CUNNINGHAM It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the claims, claim l2 should be dependent on claim ll Signed and sealed this 10th day of October 1972.

(SEAL) Attest:

EDWARD MlFLETCHEmJR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents

Claims

1. A circuit for supplying a series of timed current pulses to a work coil which comprises: a timing circuit means for receiving a DC current from a power sOurce and for supplying current pulses of such power, said timing circuit means including release means for releasing current from said power source and trigger means for causing the release of current by said release means in response to power from said power source, said trigger means being connected to said release means, said release means and said trigger means both being connected to said power source, said release means being responsive to a current supplied to it in opposition to a current released through it from said power source so as to no longer release current from said power source, a resonant circuit means for receiving current released by said release means connected to said release means so as to receive such current, said work coil forming a part of said resonant circuit means, said resonant circuit means being capable of developing a resonant current in opposition to the current released to it by said release means, which resonant current will be fed back to said release means to cause said release means to no longer current to said resonant circuit means until said trigger means again actuates said release means.

2. A circuit as claimed in claim 1 wherein: said release means is a silicon-controlled rectifier.

3. A circuit as claimed in claim 1 wherein: said trigger means is a trigger circuit including a resistor, a capacitor and a trigger diode, said resistor, said capacitor and said diode being connected so that said capacitor is charged by current from said power source which has passed through said resistor to a sufficient extent to cause said diode to become conductive, said diode being connected to said release means so as to cause actuation of said release means when said diode becomes conductive and passes a current.

4. A circuit as claimed in claim 1 wherein: said resonant circuit is an LC tank circuit having inductance of one leg thereof and having a capacitance and said work coil in the other leg thereof.

5. A circuit as claimed in claim 1 wherein: said release means is a silicon-controlled rectifier, said trigger means is a trigger circuit including a resistor, a capacitor and a trigger diode, said capacitor and said diode being connected so that said capacitor is charged by current from said power source which has passed through said resistor to a sufficient extent to cause said diode to become conductive, said diode also being connected to the gate of said silicon-controlled rectifier so as to pass a current to said silicon controlled rectifier when said diode becomes conductive, the base of said silicon-controlled rectifier is adapted to be connected to said power source, the cathode of said silicon-controlled rectifier and said capacitor are connected to said resonant circuit means, said resonant circuit means is an LC tank circuit having an inductance in one leg thereof and having a capacitance and said work coil in the other leg thereof.

6. A circuit as claimed in claim 5 wherein: said resistor is a variable resistor.

7. A circuit as claimed in claim 1 wherein: feedback means coupled to said resonant circuit means and operatively connected to said trigger means for controlling the operation of said trigger means in response to current pulses in said resonant circuit means so that the frequency of current pulses in said resonant circuit means remains constant.

8. A circuit as claimed in claim 7 including: a photosensitive resistor connected to said trigger means so that power to said trigger means passes through said resistor and wherein, said feedback means includes means for receiving power from said resonant circuit means coupled to said resonant circuit means and an illumination source operated thereby, said illumination source being located so that the illumination therefrom controls the resistance of said resistor.

9. A circuit as claimed in claim 1 including: a second of said timing circuit means and a second of said resonAnt circuit means connected thereto, said second resonant circuit means including another work coil, said trigger means of said second timing circuit means being connected to said release means of the first-mentioned timing circuit means so as to be actuated thereby, allowing the release means of the second timing circuit means to release a current in response to current released by said release means of said first-mentioned timing circuit means.

10. In an apparatus for induction heating in which a current from a power supply is passed to a work coil through intermediate circuitry the improvement which comprises: said intermediate circuitry consisting essentially of a timing circuit means and a resonant circuit means, said timing circuit means being connected to said power supply and to said resonant circuit means so that power is supplied to said resonant circuit means through said timing circuit means, said resonant circuit means including said work coil as a part thereof, said timing circuit means being capable of releasing a current to said resonant circuit means, said resonant circuit means being capable of resonating in response to current released to it through said timing circuit means so as to develop a resonant current in opposition to the current supplied to it through said timing circuit means, said timing circuit means being responsive to the resonant current developed in said resonant circuit means so as to no longer supply a current to said resonant circuit means until said timing circuit means is actuated so as to release current to said resonant circuit means because of power supplied to it from said power supply.

11. A process of induction heating in which current from a power supply is used to supply power to a work coil in which the improvement comprises: using said power supply to supply current to actuate a discharge means so that it will pass the current supplied to it to a resonant circuit including said work coil, causing said resonant circuit to develop a resonant current in opposition to the current passed by said discharge means and thereafter using said resonant current to render said discharge means incapable of passing a current from said power supply until said discharge means is again actuated by current supplied by said power supply and automatically repeating the steps herein specified at intervals as determined by the circuit components employed.

12. A process as claimed in claim 13 wherein: said discharge means is a silicon-controlled rectifier and said discharge means is actuated by a trigger means connected to said silicon-controlled rectifier and to said power supply, said trigger means also being connected to said resonant circuit.

13. A process as claimed in claim 11 wherein: said current pulses have a wave shape as indicated in FIG. 5 of the drawings.