JPH06500150A - Apparatus and equipment for induction hardening of machine components with precise power output control - Google Patents

Abstract

An induction hardening machine for contour hardening of machine components such as gears includes a phase angle detector circuit (112) which produces a pulse for each corresponding detection of a predetermined phase angle of an AC signal. A start switch (SW2) and the pulse produced by the phase detector provide inputs to a circuit (116) which requires concurrence of the pulse and activation of the switch before a predetermined width signal pulse is produced. The predetermined width signal pulse activates power switching devices (114) to supply a predetermined power signal to an RF generator (120) coupled to an induction heating coil (128). Precise induction heating is accomplished via precise control of power input to the RF generator (120).

Description

[Detailed description of the invention] Apparatus and method for induction hardening of machine components with precise power output control consecutive applications) This application is based on a pending U.S. patent application filed on August 6, 1990 based on the same inventive concept. Request cylinder 071563, 398 r Apparatus and Method Induction-Hardenjng Machfne Comp'.

ncnts With Precise Power 0output Cont This is a partial #continuation application of rolJ.

(Technical field) The present invention relates to induction heating technology, particularly for case hardening of mechanical components such as gears. Learn how to use induction heating equipment.

(Background technology) Machines such as gears, splined shaves and sprockets Mechanical components are often subjected to high torque loads, frictional fatigue and shock loads.

This type of gear is typically used in drive trains of power transmission devices. this Apparatus and methods for induction hardening of machine components such as Storm et al., U.S. Pat. No. 4,845,328, cited in the text for has been done. Both the Storm et al. patent and this application are from the same assignee. Contour Hard in Indiana, USA Owned by ening company.

As is well known in the art, known devices for hardening gear toothing include low frequency Electric current is used to preheat the gear teeth, and then high frequency (radio frequency) current is used to preheat the gear teeth. 2 for induction heating used for final heating prior to quench hardening of the dentition. Includes frequency equipment. Regarding this two-frequency induction hardening concept, please refer to the paper rlnd uction Gear Hardening by the Dual-Fr equivalence MethodJ (Heat Treating Magaz ine, Volume 19, No. 6, June 1987).

As explained in the paper, the dual-frequency heating method uses high-frequency and low-frequency reheat sources. use the Gears are first powered by the energy required to preheat the entire tooth row of the gear. is heated inductively with a relatively low frequency source (3-10 KHz) that provides this Immediately after the process, typically 1 Induction heating follows with a high frequency source ranging from 0.00 to 300 KHz. high frequency solenoid The final heat is applied rapidly to the contour surface of the dentition to the case hardening temperature. Then the gears are in place It is rapidly cooled and tempered to a hardness of .

Induction heating is the earliest known method of heating ferrous alloy gears. for a certain purpose In some cases, a preheating low frequency heating process precedes the final heating RF heating. High frequency R The heating time for the F heating step is typically in the range of 0.10 to 2.0 seconds. . In induction heating, the gear is mounted on the main shaft and the gear is mounted inside the induction heating coil. rotated while Fast pulses of power are delivered to the induction heating coil, which heats the gears. Obtain optimal final heat of the dentition. Next, the workpiece is quenched manually or automatically with water. Moved to bath. Induction hardening provides the necessary amount of heat to the part, so it is hardened. Depth requirements and strain specifications are met with great accuracy.

In the induction heating process, whether dual frequency or single frequency, In addition, regardless of the type of component or its material, the characteristics of the component may differ depending on the induction heating coil and the requires optimal design of both appropriate machine settings. In particular, high frequency power signals generate final heat. The number of hours supplied to the induction heating coil to achieve this is the most critical parameter.

A power signal is supplied to an induction heating coil to generate the exact amount of heat needed to harden the gear. Directly related to the exact number of hours.

Traditionally, in the technology for powering induction heating coils such as those mentioned above, Two systems are known. The first system is a “solid-state” We use what is known in the art as the Nerator method, in which bipolar A high power amplifier device such as a transistor or CMO8 generates a high frequency oscillation signal. used in high frequency RF generators to supply signal to induction heating coils .

Another attempt uses a vacuum tube RF generator to create a high-frequency, high-power vacuum tube oscillation circuit. is to use a Cyrisk-style device to turn on/off power to .

The output of both oscillator circuits is connected to the induction heating coil by a transformer. metal structure Some expertise in the technology of induction heating coil devices designed for case hardening structures. Homes have traditionally been made more flexible due to precise, all-in-time control of the power supply to induction heating coils. has been favoring a high-frequency RF generator. vacuum tube RF generator is typically referred to as a reverse blocking triode siren, also in the JEDEC description. Thyristor devices such as silicon controlled rectifiers (SCRs), also known as thyristor receives its input power, which is affected by the on/off timing characteristics of the device. SCR The power delivery timing variations caused by belongs to. In particular, -HsCR is kept "on" for partial cycles. , even if the on/off signal applied to the gate is removed or deactivated. Also, as long as the anode to cathode terminal is biased with a positive voltage, the SCR will carry a current will continue to go through. The maximum of 60 cycles of power signal transmitted by SCR Even in the bad case, since half of the 60-cycle waveform is 8,33 milliseconds continuous , 8 milliseconds or more, resulting in another power signal being conveyed by the SCR.

When a vacuum tube RF generator supplies power to an induction heating coil, its characteristic Due to the power supply curve, induction heating technology may be preferred by some. Is recognized. Additionally, SCR is a device that selects repeated high-power switching circuits. Since the S Techniques are needed to accurately control CR.

For more precise control of the timed power output of silicon-controlled rectifier power supplies. The method and equipment are This is necessary to accurately control the force signal.

(Summary of the invention) For induction hardening of machine components with precise control of power output according to the invention The device is connected to an AC power source that generates an AC power signal and that is connected to the AC power source to generate an AC power signal. a zero-crossing detection device for detecting zero-crossings of and generating a responsive zero-crossing signal; Generates a high frequency, high power signal in response to a power input and a signal applied to the power input. A high-frequency generator with an output that fits the gear, and a generator with dimensions that fit with the gear. a high-frequency induction heating coil connected to the output of the a power input and a The power switching device includes a thyristor power switching device having a power output. an AC power signal at the power output in response to a signal applied to the excitation input; Connected to the zero-crossing detector and the excitation input of the thyristor power switching device includes a processor device that calculates the excitation time and provides a corresponding excitation signal to the excitation input; Look, this processor device is 1) a device for inputting a predetermined excitation time; and 2) a device for inputting a predetermined excitation time; and 2) an AC power 3) a device for calculating a delay time corresponding to a minimum integral multiple of a signal period; and 3) a user device. an input device for receiving a manual cycle initiation input signal provided by the processor; The sensor device detects the zero-crossing signal and determines whether the excitation signal is equal to or greater than a subsequent zero of the AC power signal. A delay time before applying the excitation signal to the excitation input so that it is deenergized approximately simultaneously with the crossing. in response to the cycle start input signal by delaying the cycle start input signal by a period equal to .

An induction hardening apparatus according to another aspect of the invention includes an AC power source that generates an AC power signal; , a phase detection device for detecting a predetermined phase angle of the AC power signal; The power generator generates a detection signal when a predetermined phase angle is detected, and the power input and power A power that produces a high frequency, high power signal at the power output in response to a power signal applied to the input a high-frequency generator device δ having an output and a high-frequency induction generator connected to the power output; a heating coil that generates a high frequency electromagnetic signal in response to the high frequency high power signal. includes a power switching device that emits a power signal and is connected to an AC power signal; The switching device includes an excitation input, and the power switching device has an excitation input. responds to the detected signal by providing an AC power signal to the power input upon receipt of the signal at the and a timer circuit arrangement that provides an excitation signal of a predetermined duration to the excitation input. nothing.

According to another aspect of the invention, an AC power source and a high frequency generator having a power input. and a high-frequency induction heating coil. The control method is to detect a predetermined phase angle of the AC power supply, and to detect the predetermined phase angle. connects an AC power source to the power input of the high frequency generator for a predetermined period of time in response to including steps to

In accordance with yet another feature of the present invention, precise control of the power supply to a high frequency induction heating coil is achieved. The induction hardening equipment uses an AC power source that generates an AC power signal and a a first circuit arrangement that generates a first signal in response to detection of a defined phase angle; and a switch. a switch device that generates a starting signal when the electrical generator is energized; a first signal and a starting signal; a second for generating an excitation signal of a predetermined duration in response to the simultaneous occurrence; a circuit device that produces a high frequency, high power signal in response to a signal provided to the power input. A high frequency generator device having a power input and connected to an AC power signal and having a predetermined supplying an AC power signal to the radio frequency generator in response to the excitation signal of a predetermined duration; and a power switching device.

One object of the present invention is to provide an improved induction hardening machine.

Another object of the invention is to control the power signal supplied to the induction heating coil of an induction hardening machine. Proposal of a method to precisely control the heating of gears during case hardening by more precise control. It's with me.

Another object of the invention is to further improve the accuracy of the total power output signal so that it can be controlled with greater precision. The objective is to provide a reliable high power switching circuit.

These and other objects of the invention will be further described in the following description of the preferred embodiments. will become clear.

(Brief explanation of the drawing) FIG. 1 is a block diagram of a typical embodiment of an induction hardening system according to the present invention. 2 is the active state of the SCR for certain input conditions supplied to the gate of the SCR, i.e. Timing diagram showing variations in the "on" state, Figure 3 compared with prior art device changes in the power output signal caused by the electrical switching SCR circuit of the present invention. FIG. 4 is a graph showing the dynamics of another embodiment of the induction hardening system according to the present invention. It is a lock diagram.

(Example) For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and a description thereof will be provided. Specific terms are used for clarity. However, this is not intended to limit the scope of the present invention. Not shown are changes and further modifications in the illustrated apparatus and shown in the examples. Further applications of the principles of the invention, such as those described herein, will normally occur to those skilled in the art to which the invention pertains. It will be understood that

Referring now to FIG. 1, an induction hardening system 10 according to the present invention is shown. Swish The SWI sends an excitation signal to the system process to induce or initiate case hardening of the gear. provided to the server 12. System processor 12 determines the timing parameters. programmed by the user to control the power signal supplied to the induction heating coil using grammed. Processor 12 converts the on/off power switching signal into electrical switches. It is applied to the switching SCR circuit 14. System processor 12 performs zero-crossing detection. 16 receives a zero-crossing indicator input signal from device 16. 3b One digit from high voltage power supply 18 are applied to the inputs of zero-crossing detector 16. This 3b high voltage power supply 18 is Three-phase high voltage power is supplied to the electric switching SCR circuit 14. system Processor 12, when excited, receives either a half-wave or full-wave AC power signal. It is supplied to the primary winding of the step-up transformer 22. Transformer 22 is typically 480 port The rectifier and filter 24 converts the AC power signal S, b2, b, which is a three-phase signal of It is boosted to a voltage level that produces a 24,000 volt DC signal at its output.

This 24.000 volt DC signal at the output of the rectifier 2;) filter 24 is: This is the power source for a high energy RF oscillator 26 in the form of a vacuum tube. High energy RF emission The output of the vibrator 26 is connected via a winding 29 to an induction heating coil 28 . induced addition The heating coil 28 transmits the case hardening heating signal to the gear 3 when the RF multiplied signal is applied to its input. 0 gear tooth row.

Components 22.24.26 of system 10 are high frequency, high power RF generators. This is a part of the RF generator 20. The RF generator 20 is manufactured by Wisco, USA. Mcnomoncc Falls, Mcgal Drive, N92W 15,800 systems supplied from time to time by Pillar Industries, Inc. 1, this RF generator 20 is r450/600 kilowatts R It is called "F generator". .

The specific shape and physical attributes of gear 30 are electrically controlled to produce a suitable case hardening result. Customizing SCR circuit 14 is turned “on” by system processor 12. request the exact amount of time to be spent. In some cases, when the SCR circuit 14 is turned on The interval should be as short as 0.10 seconds in order to obtain the specified heating and case hardening of the gear 30. It is a long period. With these conditions in mind, it is possible to Why is the amount of power signal supplied to the induction heating coil 28, i.e., the total power It is easy to see if the force could not be controlled accurately.゛Main departure The system processor 12 typically has extensive memory and computing power. a computer with a computer and a programming input device such as a CRT/keyboard device Contains. Additionally, the processor 12 is capable of storing and retrieving control programs. A floppy disk drive or hard disk drive used in It has a mass storage device such as a drive. In operation, electric switching S CR circuit 14 provides a fixed amount of high frequency power signal to induction heating coil 28 a specific "on time" or heating time, which is the exact time at which it should be switched on for , the operator programs the system processor 12 via the keyboard. Ram. In response to this programmed “on time” information, the system During the “on time” during which the processor 12 is divided by 8.33 milliseconds (60Hz waveform period) Compute the complement value for a particular "on time" equal to the difference between . The remainder from this calculation The remainder is subtracted from 8.33 ms to power the RF generator. Prior to exciting the CR circuit 14, the 60 Hz signal present at the input of the detector 16 is After detecting the crossing, processor 12 generates a time value that is the delay time to be delayed. . This time delay calculation is based on the fact that the end of the on or conduction period for the SCR circuit The power signal supplied to the input of the zero-crossing detector 16 is detected at or just after the zero crossing. is intended to correspond exactly to the previous one. Therefore, the cathode terminal from the anode An SCR that remains conductive as long as it is forward biased is The circuit 12 interrupts the SCR circuit 14 by deenergizing the input to the circuit 14. It does not remain on for a practical period of time after being signaled to disconnect.

In this technology, the SCR circuit 14 converts the half-wave or full-wave 3b output signal into a transformer. 22 is well known. If the nature of this signal is half wave, then the above The divisor (8.33 milliseconds) is 16.67 milliseconds, and the remainder is 16.67 milliseconds. will be deducted from Additionally, a suitable timing basis for exciting the half-wave output SCR circuit is provided. Zero crossings of the negative slope must be detected to determine the quasi-point. For this reason, The given "on time" is divided by 16.67 and the remainder is subtracted from 16.67. It will be destroyed. The result of this subtraction process is the SCR circuit 14 to produce a half-wave output. is the delay period required after the zero crossing of the negative slope of the power signal before exciting the power signal. Ru. The other phases of SCR circuit 14 (bz and bs) are connected when the input to circuit 14 is turned off. The above method maintains the "on" state even after the SCR circuit 14 is activated. produces accurate and repeatable power output.

Referring now to FIG. 2, the active state or "on" state of the SCR for a certain gate signal condition A timing diagram is shown showing changes in state. The car 140 is connected to the detector 16. A standard sinusoidal power signal representing the b1 signal at the input. The car 140 is 60 horizontal signals plotted over time. Curve 42.46 is the system a signal generated by the program processor 12 and applied to the gate input of the SCR circuit 14; represents. Curves 42, 46 are for a particular gear 30 to be induction hardened. This is the “on time” required to generate a predetermined amount of heat.

The circuit 14 is energized or jittered at some point during the off/on transient of the curve 42. A power signal is supplied to the generator 20. “On time” of curve 42 At the end of time TI, the signal changes from the "on" state to the "off" state. O The exact timing of the on/off transients occurs near the zero crossing of curve 40. do not have. After the excitation signal represented by car 142 crosses zero at time Tc, The curve given to the RF generator 20 The power signal represented by 44 is 8.3 after the on/off transient of curve 42. It remains "on" continuously for a time T, which can be as long as 3 milliseconds. For this reason, An on signal generated by system processor 12 begins at time TI1 and continues at time T.

If the graph continues until It continues for the entire period T2 from time T, until time T, when the process begins.

To precisely control the power supplied to the induction heating coil and thereby In order to obtain more precise control of the quenching process, the system according to the invention The SCR excitation signal represented by 46 is at or just before the zero crossing of Kerr 140. The SCR circuit 14 is turned on so that it changes from an "on" state to an "off" state. Calculate the time delay beyond the zero crossing (in this example, the zero crossing at To) to do. For example, a gate on switch represented by curve 42 switching an SCR circuit. To remove the additional "on time" of the power signal 44 compared to the time input signal, the system The system processor 12 calculates a predetermined "on time JT+" divided by 8.33 milliseconds. Compute the corresponding time T, and subtract the remainder from 8.33 ms to produce time T3. Jiru. Next, the system processor calculates curve 42 and the "on time" duration. The times at which exactly equal excitation curves 46 correspond to zero crossings of curve 40 of the power signal After the zero crossing, so as to change from the "on" state to the "off" state at Tc The excitation of the SCR circuit 14 is delayed by a period T3.

Since curve 46 is very closely related to the zero crossing at time Tc, the SCR circuit 14 accurate “on-time” amounts, which allows power to be control with precision never known before. At this time, the electric current is supplied to the induction heating coil 28. The amount of power consumed is precisely controlled. This makes solid-state semiconductor formats highly Vacuum tube type RF generators are preferred by those skilled in the art as superior to frequency RF generators. Similarly, the exact quality of the power signal and the power supplied to the induction heating coil 28 It can be used to produce accurate quality.

Although only one phase (b,) of power supply 18 is shown in FIG. It will be clear that in the system the three total phases are related by 120°. others Therefore, another power signal of a fixed amount is applied over time TC by the excitation signal represented by curve 46. Beyond that, it will be supplied by the other phases of power supply 18 (b2 and bl). So Nevertheless, since the other power phases produce deactivating signals, the other two phases The additional power supplied will be of constant quality. Therefore, the system 10 causes the gear 30 to The amount of power supplied depends on the fixed timing of switching the 3b power supply on and off. can be iterated by establishing a reference point (for one phase) of .

Referring next to FIG. 3, a graph of the power output of RF generator 20 is shown. car The maximum power output of generator 20, indicated by block 50, may be higher or Can be adjusted vertically for lower total instantaneous power output. SCR circuit to the time T as a result of the inherent functionality, and the "on time" denoted by T2. The variation in is shown at the bottom of the graph. If the SCR circuit has a predetermined “on time” curve 5 if it remains on for the length of time T2 as opposed to T1. Another power represented by the hatched portion 52 below 0 is The actual value represented by the lower unhatched portion and extending to the end of time T1 In addition to the predetermined power, the induction heating coil 28 is supplied. To the induction heating coil 28 The additional amount of power supplied causes excessive heating of gear 30.

As shown in the graph of Figure 3, especially when the on time JT+ is approximately 0.10 seconds, When approaching larger variations in the case hardening process. Between time T2 and T1 The maximum difference can be as much as 8.33 milliseconds, so a 0.10 second power signal will induce When required for conductive heating coil 28, the power represented by area 52 is 8. It can represent a power difference of up to 10%. Another recognized fact is that once the gear 30 is heated When the gear is heated, the heat conduction characteristics of the gear are not linear, and once the gear is heated around the The extra heating time represented by region 52 is used to conduct more deeply into the gear surface. can significantly increase gear heat. For this reason, the method described above can be used to It is highly desirable to control the power supplied to the power source 28.

4, another embodiment of an induction hardening system 110 according to the present invention is shown. be done. Switch SW2 resets/starts single pulse timer circuit 116 give a signal. AC power supply 118 connects the AC signal to phase angle detector 112 and power source 118. Switching device 114 is supplied. The phase angle detector 112 detects a series of pulses. is applied to the input of the jil-pulse timer circuit 116. each from detector 112 The pulses correspond to detection of a predetermined phase angle of the AC power signal from power source 118 ,.

Upon receipt of the reset/start signal from switch SW2, a single pulse tie is activated. The marker circuit 116 is tested to produce a pulse or signal having a predetermined duration. The next pulse from output 112 triggers or excites. predetermined duration The pulse between enables the power switching device 114. For this reason , the start of the heating cycle as a result of the closing of switch SW2 occurs at a predetermined phase. There is a delay until the angle is detected by phase angle detector 112. Phase angle detector 1 12 is a position for detecting a predetermined phase angle in the power signal from the AC power source 118. A phase detection device is provided.

As in the previous embodiment, the RF generator 120 is a power switching device. Receives a power signal from the chair 114 and, in response, transmits a high frequency, high power signal to the winding 12. 9 to the induction heating coil 128. Winding 129 is an RF generator 120 and the induction heating coil 128. Single phase and polyphase power supplies are considered.

The phase angle detector 112 is a Tria manufactured by Motorola, Phoenix, USA. The phase angle controller is implemented using part number TDA1185A. This T The DA1185A device detects a predetermined phase angle of an AC signal and outputs a corresponding output signal. is programmable to produce This predetermined phase angle is equal to the predetermined conduction angle. can be changed by the TDA1185A device according to an externally set voltage representing . (the below described (see discussion of control signals) To detect the firing angle, even if the firing angle in the negative half of the AC signal is required, An inverting operational amplifier is inserted between the AC power source and the phase angle detector 112 to invert the AC signal. , phase angle detector 11 such that this results in excitation in the negative half of the AC signal. Give an input signal to 2.

The signal pulse/timer circuit 116 is manufactured by Texas Instruments. Retriggerable monostable multivibrator integrated circuit, part number 74LS12 This is realized using 3. This 74LSI23 is triggered by the rising edge. The pulse generated by the phase angle detector 112 is therefore a timer device. It can be used to trigger the output pulse from circuit 116. Swish The signal generated by switch SW2 is used for retriggering, enabling or re-arming. arming) signal to the timer circuit 116. 74LS123 device is 1 mi to produce output pulses with durations from less than a millisecond to very large durations, such as hours. Since the combination of phase angle detector 112 and timer circuit 116 can be configured as The tuning requires the supply of a specific duration power signal to the RF generator 120. to energize the power switching device 114 according to the previously mentioned conditions. Provides widely variable control over the required timing functions.

Any control signals represented by dashed lines 132, 134 are connected to the selected phase angle and and pulse width duration signals to detector 112 and circuit 116, respectively. . In particular, the phase angle control signal present in signal path 134 and fed to the input of detector 112 The signal provides phase angle selection information to detector 112. The signal in signal path 134 In response, detector 112 detects the predetermined signal established by the signal on signal path 134. It produces an output pulse that corresponds in time to the occurrence of the phase angle. Similarly, signal path 132 The duration control signal present in control The signal in signal path 132 is an attenuated signal, which is well known in such circuits. Typically consists of a potentiometer/capacitor combination that establishes It is.

The apparatus 110 of FIG. 4 has some components that are the same as those of the apparatus 10 of FIG. including. In particular, the AC power supply 118 corresponds to a three-phase high voltage power supply 18, and the power switch The switching device 114 corresponds to the power switching SCR circuit 14 and is connected to the RF generator. The generator 120 corresponds to the RF generator 20, and the induction heating coil 128 corresponds to the RF generator 20. Corresponding to the heating coil 28 is the gear 130, which corresponds to the gear 30. triac immediate A silicon controlled rectifier (SCR) performs power switching in block 114. ・It is considered to be a device.

In operation, the pulses produced at the output of phase angle detector 112 are It temporally corresponds to a predetermined phase angle of the AC signal indicated by the interval line T8. similar , the output pulse produced by timer circuit 116 corresponds to time T2. others The difficulty of exciting an AC power source with precise timing and power output control is , is used to determine the on-time of a power signal using the time delay after the zero crossing. 1, or as in the embodiment of FIG. to determine when a power switching device is required for excitation. The phase angle of is detected. According to both embodiments of the invention, a predetermined The defined timing reference point is when the power switching device between and typically turn off at the zero crossing as is the case in most thyristors. before or at the same time as a subsequent zero crossing of the power signal so that the AC prior to excitation of the power switching device to produce a decreasing excitation signal. A power signal is found or detected.

Alternatively, phase angle detector 112 and timer circuit 116 may be part of a computer-based controller (not shown) in which the A/D control A converter (not shown) is used to convert the amplitude (corresponding to the phase angle) of the signal from power supply 118. ) may also be considered. Furthermore, user-modifiable software , detected predetermined phase angle and supplied to power switching device 114. This enables control of the control pulse width.

Although the present invention has been shown and described in detail in the drawings and text description, this invention The examples should be considered illustrative and limiting in nature, and are not intended to describe preferred embodiments. but only as shown and described, and all changes and modifications that come within the spirit of the invention. It will be appreciated that the right is required to be protected.

Ti “-phase angle control m signal international search report Continuation of front page (81) Designated countries EP (AT, BE, CH, DE.

DK, ES, FR, GB, GR, IT, LU, NL, SE), 0A (BF, BJ, CF, CG, CI, CM, GA, GN, ML, MR, SN , TD, TG), AU, BB, BG, BR, FI, HU, JP, KP, KR, LK.

MC, MG, MW, No, PL, RO, SD, 5U (72) Inventor Gibbs, Su Spencer Elle USA 46122 for Indiana. Danville, Kata sburg road

Claims (14)

[Claims] 1. an AC power source producing an AC power signal and a predetermined phase angle of said AC power signal; a phase detection means for detecting the predetermined phase angle; generates a detection signal and has a power input and a power output, and is applied to said power input. a high frequency jet that produces a high frequency high power signal at the power output in response to the received power signal; a high frequency induction heating coil connected to the power output; The coil emits a high frequency electromagnetic wave signal in response to the high frequency high power signal, and the coil emits a high frequency electromagnetic wave signal in response to the high frequency high power signal. A power switching means is provided connected to the power signal, the power switching means an excitation input, the power switching means receiving a signal at the excitation input; providing the AC power signal to the power input in response to the detection signal; timer circuit means for supplying an excitation signal of a predetermined duration to said excitation input; of, An induction hardening device characterized by comprising: 2. the power switching means is a thyristor power switching device; The device according to claim 1, characterized in that: 3. a reset/start switch, said timer circuit including an enable input, and said timer circuit including an enable input; the reset/start switch applying an enable signal to the enable input; The timer circuit generates the signal for a predetermined duration in response to the detection signal. 3. The device according to claim 2, characterized in that: 4. Monostable multivibrator device in which said timer circuit can be retriggered 4. The device according to claim 3, characterized in that: 5. The dimensions of the high-frequency induction heating coil that correspond to the metal parts that require case hardening. The device according to claim 4, characterized in that: 6. Induction hardening equipment including an AC power source and a high frequency generator having a power input in a method for precisely controlling the power supplied to a detecting a phase angle, and in response to detecting the predetermined phase angle, the AC power source is switched to a high frequency connecting to a power input of the wave generator for a predetermined period of time; A method characterized by: 7. The induction hardening apparatus includes a start/reset switch, and further includes a start/reset switch. detecting activation of a reset switch and connecting the AC power source; Said step also equates to detecting an energized state of said start/reset switch. 7. A method according to claim 6, characterized in that the method is sometimes conditioned. 8. When the induction hardening device is excited, an AC power signal is sent to the generator. a thyristor switching device connected to a power input of said predetermined in response to the simultaneous detection of the phase angle set and the excitation of the switching. step delivers an excitation signal of predetermined duration to the thyristor switching device. 8. The method of claim 7, further comprising supplying the liquid to a chair. 9. In induction hardening equipment that accurately controls power supply to high-frequency induction heating coils. in, an AC power source that produces an AC power signal; a first signal generating a first signal in response to detecting a predetermined phase angle of the AC power signal; circuit means; switch means for producing a starting signal when said switch means is energized; a predetermined duration in response to and in response to the simultaneous occurrence of a signal and said starting signal; second circuit means for producing an excitation signal between the high frequency generator means for generating a high frequency, high power signal in response to the received signal; connected to the AC power signal and in response to the excitation signal of the predetermined duration; power switching means for supplying the AC power signal to the high frequency generator; An induction hardening device characterized by being provided with. 10. said second circuit means includes a duration input, said second circuit means includes a duration input; The activation signal is variable in duration according to the signal provided to the duration input. 10. The device according to claim 9, characterized in that: 11. said first circuit means includes a phase angle selection input, said first circuit means said generating said first signal in response to a phase angle determined in accordance with a signal appearing at a phase angle input; 11. The device according to claim 10, characterized in that: 12. the phase according to the phase angle required for excitation of said power switching means; 3. The method of claim 1, further comprising means for providing an angle control signal to said phase angle selection input. The device according to range 11. 13. said predetermined duration by providing a duration control signal to said duration input. characterized in that means are provided for allowing a variable duration of the excitation signal of a given duration. 13. The apparatus according to claim 12. 14. characterized in that the radio frequency generator produces an output signal in the radio frequency range. 14. The device according to claim 13.