MXPA97002681A - Multi head inductive heating system - Google Patents

Abstract

A system and method for inductively heating a part including a controller and a plurality of power supplies that receive and send signals to the controller. The induction heads receive the energy from the energy sources. The induction heads can be aligned as adjacent segments in the workpiece and can measure the perimeter of the workpiece. The gap between the adjacent induction heads is less than half the size of the adjacent induction heads, and preferably the induction heads are in contact or substantially in contact. Each of the energy supplies includes feedback to control the electricity or energy provided to the segments of the work piece. In alternative embodiments the feedback can be based on the current or energy provided to the induction forces, or the energy provided to the work piece

Description

INDUCTIVE HEATING SYSTEM OF MULTIPLE HEAD BACKGROUND OF THE INVENTION Technical Field The present invention relates generally to inductive heaters and, in particular, to induction heating systems having multiple heads. BACKGROUND OF THE ART Induction heating is a well-known method for producing heat in areas located in a susceptible metal object. Induction heating involves the application of an alternating current signal to a heating circuit or coil placed near a specific location or around a metal object to be heated. The variation or alternation of the current in the circuit creates a variable magnetic flux within the metal to be heated. The current is induced in the metal by means of a magnetic flux, therefore heating it. Induction heating can be used for many different purposes, including adhesive treatment, metal hardening, welding, and other manufacturing processes in which heat is a necessary or desirable agent or an adjuvant. The prior art is replete with electrical or electronic power supplies designed for use in induction heating systems, many of which have inverted power supplies. These power supply inverters typically develop high frequency signals, generally in the range of ilohertz to megahertz, for application in the work coil. Therefore, there is generally a frequency at which the heat is more efficient with respect to the work to be performed, some inverters of the prior art power supply operate at a selected frequency to optimize the heat. The intensity of the heat also depends on the magnetic flux created, therefore the induction heaters of the prior art control the expected current in the heating coil, therefore they try to control the produced heat. An example of the prior art representative of the induction heating system having inverters is United States Patent Number 4,092,509, issued May 30, 1978 to Mitchell. Mitchell describes numerous inverter circuits for the power supply of induction heaters. The circuits are designed to operate in a range of 20 to 50 kilohertz, aiming to maximize the efficiency of induction heating. Up to this point Mitchell describes the control of the magnitude of the magnetic flux, and therefore the control of the heat created by the induction heating, if they use switches to make the selection between one to two inverter circuits. For example, in Figure 40, switches 404 and 407 are moved to positions 404A and 407A, respectively, or positions 404B and 407B, respectively, to select between a high energy output and a low power output. Another type of induction heater in which the output is controlled when turning on or off the inverter's power supply is presented in U.S. Patent No. 3,475,674, issued October 28, 1969 to Porterfield et al. The average of the power output of the induction heater described by Porterfield varies according to the average time during which the inverter is off compared to the time during which the inverter is turned on. Another known induction heater utilizing an inverter power supply is disclosed in U.S. Patent Number 3,816,690, issued June 11, 1974 to Mittelmann. Mittelmann describes an induction heater that has a variable frequency inverter power supply. The operating frequency of the inverter is selected to provide maximum efficiency of the energy transferred between the output of the inverter and the inducing element used to heat the work piece. In order to provide an adequate amount of heat to the work piece, Mittelmann controls the delivery or distribution of watts / seconds at the inverter output. In response to the measurement of watts / seconds, Mittelmann selectively turns the inverter on and off. Therefore, the average heat distributed by the induction heater is controlled. Each of the above methods for controlling the delivery of energy by means of an induction heater is not adjustable in frequency and / or does not adequately control the heat or energy distributed in the work piece by means of the heater. The prior art of induction heaters disclosed in U.S. Patent Nos. 5,343,023 and 5,504,309 (also assigned to the assignee herein) provide frequency control and a way to control the heat or energy distributed to the workpiece. These induction heating systems include an induction head, a power supply, and a controller. Groups have been used, where there is a one-to-one correspondence between the induction head, the power supply and the controllers. One use of induction heaters is the treatment or cure (or partial cure) of adhesives in the automotive industry. Generally, the adhesive is provided around the perimeter of a part of the automobile, such as the door. As used in the present perimeter it means near the edge, away from the center of the workpiece, or where the adhesive is applied. An induction heater is used to cure or treat (or in some cases partially cure) the adhesive by heating the door adjacent to the adhesive. During the healing process, the door with an adhesive arranged around the perimeter rests in one place and the induction heads are placed around and / or near the workpiece. Then, the energy is supplied to the induction heads, which heat the portions of the door close to the head, and the adhesive is cured or partially cured to the desired degree. A similar application involves the use of metal-based adhesives. These adhesives have metallic substances added to the adhesive which is heated directly by means of induction. In order to properly cure the adhesive, the amount of energy provided to the work piece by means of the head must be controlled properly. This energy depends, among other things, on the energy provided to the head, the loss in the head and the relative position of the head with respect to the work piece (which affects the coupling). However, in many applications, particularly those in which the distance from the head to the work piece is controlled with difficulty, as for example in automotive applications, the distance from the head to the work piece can vary in different locations in the work piece. Therefore, it can be difficult to control the energy supply or the energy applied equally to the different portions to the workpiece to be heated. There are, at least, two arrangements of the prior art used to inductively heat a large work piece. One is to provide an induction coil with a shape that generally coincides with the shape of the part to be cured or treated. Therefore, the entire perimeter of the part (such as a car door) is heated, and the adhesive is cured along this perimeter. The other arrangement or arrangement consists of having a number of induction heads, each of which cures a selected portion or portion of the perimeter, and each is connected in series to a simple energy source. Both arrangements are described in U.S. Patent Number 4,950,348. However, both depositions or settlements have significant flaws. Both provide a simple current (either to each part of a head, or to each part of several heads). If the door or other parts are not located precisely in the isolated place, the heat relative to the distance of the work piece may vary along the perimeter of the part, and the heat (or energy or power) provided to the work piece is not uniform around it, therefore it is not get the desired heat. Also, the arrangement or arrangement "of healing of points" is not desirable because it cures the entire perimeter, and therefore the cure is not uniform. Thus, it is desirable to provide a method and apparatus that inductively heat the workpiece using multiple heads, each of which can be separately controlled to provide the desired heat. Additionally, it is preferable that this method and apparatus be capable of inductively heating a complete perimeter of a workpiece. Moreover, it is preferable that the multiple induction heaters heat the perimeter to be controlled separately, so that a more uniform heating can be obtained. Additionally, prior art controllers used in the area of induction heating are not provided with adequate failure warnings. Generally, the prior art simply provides a fault light that illuminates during the heating cycle if a fault is detected in this cycle. While it may be appropriate to indicate the existence of a problem, the indication that there is a problem or how this problem can be solved is not provided. Accordingly, it is desirable to provide an induction heating system having a fault detector and record the faults so that appropriate adjustments can be made. SUMMARY OF THE INVENTION A system for inductively heating a workpiece according to one aspect of the invention comprises a controller and a number of power suppliers that receive and send signals to the controller. A number of induction heads receive the energy of one of the energy suppliers. According to a second aspect of the invention the induction heads are aligned with the adjacent segments of the workpiece to be cured. In another alternative, the induction heads cover the perimeter of the work piece. The gap or distance between the adjacent induction heads is less than a half the size of the adjacent induction heads, and preferably the induction parts are in contact or substantially in contact. The third aspect of the invention is that the controller and each of the power supplies include a feedback to control the energy provided to the segments of the work piece. In an alternative embodiment the feedback can be based on a current or energy provided to the induction heads, or the energy provided to the work piece. A fourth aspect of the invention is a method for inductively heating the work piece. The method includes aligning a plurality of induction heads with segments adjacent to the work piece providing the power to each of the induction heads, wherein the distance or gap between the adjacent induction heads is less than a medium of the size of the adjacent induction heads. In other embodiments, the induction heads are connected to one or more energy sources and each of the energy sources is controlled. A fifth aspect of the invention includes the above method, including the step of aligning the induction heads with the adjacent segments of the perimeter of the workpiece to be cured and the distance from the perimeter of the workpiece. The feedback is used to control each of the induction heads in another aspect of the invention. In alternative embodiments the feedback can be based on the energy provided to the head, or the energy provided to the work piece. Another aspect of the invention is an induction heating system with a continuous segmented perimeter. The system can include feedback, and can cover the entire perimeter of the work piece. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram in an induction heater; Figure 2 is a circuit diagram of the energy inverter shown in Figure 1; Figure 3 is a circuit diagram of the frequency of the inverter shown in Figure 1; Figure 4 is a block diagram of a multiple head induction heater constructed in accordance with the present invention; and Figure 5 is a flow chart showing the operation of the controller according to the present invention. DETAILED DESCRIPTION OF A PREFERRED EXEMPLARY FORM OF EMBODIMENT Before explaining at least one embodiment of the invention in detail, it is necessary to understand that the invention is not limited in this application to the details of construction and the arrangement of the components established in the following description as illustrated in the drawings. The invention is capable of having other embodiments, ways of practicing or of carrying out and it should be understood that this preferred embodiment is one of many embodiments. Also, it should be understood that the phraseology or terminology used herein is for description purposes and should not be considered as a limitation. The present invention relates to an induction heater and heating systems such as those used to cure adhesive to stick a piece of metal to another object. The system can include multiple heads and power supplies to provide control of the energy distributed to the workpiece, and preferably, includes a fault detector and a recording system. Generally, the use of multiple heads with multiple power supplies and a single controller in accordance with the present invention can be realized with a wide variety of feedback mechanisms and controllers. However, it is referred to below, for the purpose of completing it, an example of a controller and an energy circuit. The specific controller and the feedback system described should not be considered as a limitation. Referring to Figure 1 an induction heater, generally designated 100, includes an energy inverter 102, an output inverter 104, an induction head 106, a controller 108, and couplers lio and 112. It is also indicated in FIG. Figure 1 a workpiece 116, whose induction heater 100 heats up, and a DC power source 114. In operation, the power inverter 102 receives the DC current from the DC power source 114. Alternatively, the power source can be an alternating current (AC) power source and a rectifier may be provided, such that the power inverter 102 receives a rectified alternating power supply. The power inverter 102 then reverses the supplied DC power signal and controls the wide inverted signal pulse by modulating the inverted signal (also called inverted signal control phase), and therefore provides an AC signal at a first frequency that it is high enough to respond quickly to the feedback signals (but preferably not so fast to cause voltage in the inverter components). The coupler 110 then rectifies the AC signal to provide a second DC signal having a magnitude depending on the amplitude of the pulse or the modulation phase of the AC power signal of the inverter 102. The second DC signal, the output of the coupler 110, it is applied to the output of the inverter 104. The output of the inverter 104 inverts the DC signal at a selected frequency to optimize the heat provided to the induction head that is being used. The frequency can be an established factor, adjusted by the user, or depending on the LC time constant of the circuit output (which includes an induction coil and capacitors). The magnitude of the AC signal depends on the magnitude of the DC input signal, and therefore it responds to the wide pulse modulation of the power inverter 102. The AC signal is transformed by means of the coupler 112 and is applied to the head induction 106. AC current through induction head 106 induces current in workpiece 116, therefore, causes the workpiece 116 to be heated in a location adjacent to the induction head 106. The intensity of heat produced in the workpiece 116 depends on the magnetic flux induced in the workpiece. The magnetic flux is turned on in response to the magnitude of the signal provided by the output inverter 104, and therefore also is in response to the modulation phase of the energy inverter 102. The controller 108 is provided to control the wide modulation. to the pulse of the power inverter 102, and the operating frequency of the output inverter 104. Referring now to Figure 2, the power inverter 102 is shown together with a three phase rectifier 202. The power inverter 102 is shown to include a plurality of MOSFETs Q1-4, a plurality of capacitors Cl-C10, a plurality of diodes D1-D8, a plurality of resistors R1-R7 and an inductor Ll. A DI transform, which is part of the coupler 110 is also shown. In phase three rectifier operation 202 preferably provides up to 100 amps at 1200 volts to rectify a voltage of 460 volts, the three-phase AC signal. In general there are two mutual exclusive current patterns to provide a first current flow in one direction through the primary transformer TI and then in the opposite direction through the primary of the transformer TI. The current pattern is: first, from the positive output of the three-phase rectifier 202 through the MOSFET Ql, the capacitor C5, the primary of the transformer TI, the MOSFET Q4, and back to the negative output of the rectifier; and second, from the capacitor C5, through the MOSFET Q2, MOSFET Q3, the primary of the transformer TI and back to the capacitor C5. This path is selected by turning on the MOSFET Q1 and Q4 and turning off the MOSFET Q2 and Q3, or in conversion, turning on the MOSFETs Q2 and Q3 and turning off the MOSFETs Q1 and Q4. In operation capacitor C5 is charged at approximately 325 volts, or a power supply medium of 650 volts. Therefore, when the MOSFETs Ql and Q2 are turned on, an ignored voltage falls on the MOSFETs Q4 and Q1, approximately 325 volts (a supply of 650 volts minus 325 volts through capacitor C5) is applied to the primary of the CT transformer , with an upper terminal of the primary that which is supposed to the lower terminal. When the MOSFETs Q2 and Q3 turn on and the MOSFETs Ql and Q2 turn off, a voltage of approximately 325 volts is applied across the primary of the CT transformer in an opposite direction. Capacitors C6 and C9 are provided to connect the voltage between the MOSFETs Ql and Q3 to 325 volts, or a half of the rectified output. When the MOSFETs Q2 and Q3 are turned on, the voltage between the MOSFET Q2 and the capacitor C5 is linked to the voltage at the common node of the MOSFETs Q2 and Q3 and the capacitors C6-C9, or approximately to 325 volts. The voltage across capacitor C5, which is a polypropylene capacitor of 8 microfarads high current, is 325 volts, and due to the high capacitance of capacitor C5, it will not charge quickly. Therefore, the voltage applied to the top of the primary of the CT transformer is zero volts. Also, through the MOSFET Ql and the C6-C9 capacitors, 325 volts are applied in the lower part of the primary of the CT transformer. Therefore, turning on the MOSFETs Q2 and Q3 results in an energy of 325 volts that is applied to the CT transformer, but in the reverse direction of the 325 volts that are applied when the MOSFETs Ql and Q4 are turned on. In order to modulate the pulse magnitude, or phase control, the signal applied to the transformer primary TI, and to the MOSFETs Q1 and Q2 is turned on and off at a constant frequency, preferably at approximately 50 kilohertz. The MOSFETs Ql and Q2 have a phase shift of 180 degrees and each has a duty cycle of 50%. MOSFETs Q3 and Q4 also have 50% duty cycles and a 180 ° phase shift between them. Also, the MOSFETs Q3 and Q4 are enslaved to the MOSFETs Q2 and Q1, respectively, since they can be turned on from 0 to 180 degrees of phase shift with respect to the respective time when the MOSFETs Q1 and Q2 are on. Since a pulse is applied to the primary of the CT transformer only when both MOSFETs Ql and Q2 are turned on, or when both MOSFETs Q2 and Q3 are turned on, the phase of the MOSFET Q2 relative to the MOSFET Ql and the MOSFET phase Q3 in relation to the MOSFET Q2, determines the pulse amplitude of the signal applied to the primary of the CT transformer. Since the MOSFETs Q3 and Q4 have a phase shift of 180 degrees between them, each is out of phase with respect to the MOSFET Q2 and Q1, respectively, by an identical amount. For example, when the MOSFET Q3 has a phase shift of zero degrees with respect to (phase amplitude) MOSFET Q2, the MOSFET Q3 will be in half cycle of the ON MOSFET Q2, and a pulse will be applied for the entire half cycle of the primary of the transformer YOU. Also, if the MOSFET Q3 is in phase with the MOSFET Q2, then the MOSFET Q4 will be in phase with the MOSFET Q1, and a pulse will be provided for all of the other half cycle to the primary of the CT transformer. In conversational form, when the MOSFET Q3 has a phase shift of 180 degrees with respect to the MOSFET Q2, the MOSFET Q3 will be out of the entire half cycle in which the MOSFET Ql is turned on, and no pulse will be applied to the primary of the CT transformer . Again, the MOSFET Q4 will also have a phase shift of 180 degrees with respect to the MOSFET Ql and no pulse will be provided in the other half cycle. In general, because the MOSFET Q3 is out of phase with respect to the MOSFET Q2 by the same amount as the MOSFET Q4 is out of phase with respect to the MOSFET Q1 in the stopped state of the operation the pulses of opposite polarity will have the same amplitude. Therefore, the pulse amplitude of 325 volts applied to the primary of the transformer TI depends on the phase of the MOSFET Q4 with respect to the MOSFET Ql and the phase of the MOSFET Q3 with respect to the phase of the MOSFET Q2. Accordingly, to control the entire output current of the current inverter 102, the controller 108 which may include a conventional pulse amplitude modulator, applies signals to the inputs of the MOSFETs Q1-Q4 and controls the phase of the MOSFETs Q3 and Q4 with respect to the MOSFETs Q2 and Ql. Alternatively, the controller 108 may include a plurality of timers such as CMOS 4098 dual timer, available from Harris Semiconductor, and a flip-flop, to provide control of the MOSFETs Q1 and Q2. To provide control of MOSFET Q3 and Q4, which are enslaved to Q2 and Q1, it can be used in a comparator, which has its output connected to the flip-flop and has as output an access to the generator and a signal that has a magnitude depending on the desired phase different between the MOSFETs Ql and Q2 and Q4 and Q3. Therefore, the impulse can be narrow or wide, although in the stopped state of the operation all the MOSFETs have a duty cycle of 50%, to ensure that the high heat does not appear in the MOSFET Ql and Q4 to protect the components . It may be desirable to provide a dead band, where, for example, when the Ql or Q3 is turned on, there is a slight delay since the Q2 or Q4 are turned off respectively, so that Q2 or Q4 will be completely off before Q1. and Q2 are on. The capacitors C1-C4 are small polypropylene retention capacitors and the diodes D1-D6 and the resistors R5 and R6 are provided to protect the MOSFETs Q1 and Q4. The capacitors C6 and C8 are large electrolytic capacitors, typically 1700 microfarads and separate the voltage provided by the three-phase rectifier 202 to a half of the voltage supplied at the common node for the MOSFETs Q2 and Q3. The C7 and C9 capactiores are high-flux polypropylene capacitors of 8 microfarads, provided to smooth the voltage seen at the common node for the MOSFETs Q2 and Q3. The diodes D7 and D8 and the resistor R7 and the inductor Ll, together with the CIO capacitor are provided to prevent an unbalance in the common node for the MOSFETs Q2 and Q3. Specifically, when capacitors C6 and C7 have a voltage across them that is different from capacitors C8 and C9, inductor Ll acts as a separation inductor and causes the voltage across capacitors C6 and C7 to become equal to which is through capacitors C8 and C9. Resistors Rl and R4 protect the input of the MOSFETs Ql and Q4. The coupler 110, the output inverter 104, the coupler 112 and the induction head 106 are now shown in reference to Figure 3. The coupler 110 includes the transformer Cl, a plurality of diodes D9-D12, a voltage regulator VR1 , and a Cll capacitor.

The primary of the CT transformer is connected to the output of the power inverter 102. As described above, the primary of the CT transformer receives a modulated AC signal of pulse amplitude at a desired frequency, exemplified herein as about 50 kilohertz. The amplitude of the pulses is determined by means of the phase controller 108 as described above. The secondary of the transformer DI is connected to the bridge of the diode comprising the diodes D9-D12, which rectify the AC signal. The rectified signal is applied to the capacitor Cl causing a voltage across it. The voltage regulator VRl is provided to ensure that the voltage across the capacitor Cll is not greater than the predetermined limit, selected to protect the inverter components. The voltage across the capacitor Cll is directly responsible for the total current induced in the secondary of the CT transformer, which is responsible for the amplitude of the pulses generated by the power inverter 102. The DC voltage through the capacitor Cll it is provided as a DC input for the output of the inverter 104. The output inverter 104 may be a conventional inverter operated at a preset or user adjustable frequency, for example, between 10 kilohertz and one megahertz, but preferably between 25 kilohertz and 50 kilohertz. The frequency range can be higher or lower, depending on the user's performance of the induction heater. Accordingly, the output inverter 104 may include transistors Q10 and Q13 and capacitors C12 and C17. Transistors Q10 and Q12 turn on and off in unison and transistors Qll and Q13 turn on and off in unison. Moreover, as long as transistors Q10 and Q12 are on, transistors Qll and Q13 will be off. It will be necessary to provide a band bite on it, before turning on a pair of transistors, the other pair will be allowed to remain off. The controller 108 provides the appropriate on and off signals by the gates or inputs of transistors Q10-Q13. Capacitors C12 and C15-C17 are provided to eliminate the loss of the switch when transistors Q10 and Q13 are turned off. The capacitors C13 and C14 are provided to block the DC current through the output transformer T3 to prevent saturation of the transformer T3. The output of the output inverter 104 is provided to the coupler 112. The coupler 112 includes a current feedback device 301, which is a faeuric toroidal core with a secondary twist sixth and a primary simple twist. The primary simple turn is connected to the transformer primary T3. The output of the current feedback device 301 is provided to the controller 108 from which it adjusts the pulse width of the energy power inverter of the energy inverter 102 in the conventional manner. In addition to the current feedback, a voltage feedback can be provided to the controller 108. The controller 108 can thus determine the power (voltage multiplied by current) delivered or distributed to the induction head 106. The controller 108 can determine the loss of heat in the induction head 106 due to the resistance of the induction head, which will be the square of the current, multiplied by the resistance of the induction head 106. The difference between the distributed energy and the energy loss in the induction head is equal to the energy provided in the workpiece 116. Multiplication can be carried out using known multiplier chips such as a MPY634 KP, Burr Brown available chip, and the subtraction can be carried out with a Operational amplifier (op amp). The output of the output inverter 104 is provided through the primary output of the transformer T3, which preferably can be a coaxial transformer, and induces a current in a secondary output of the transformer T3, which is a two-door circuit that the induction head 106 is applied in a mode or embodiment. Accordingly, as the output inverter 104 drives the current through the transformer primary T3 at an operating frequency, the current of the same frequency is induced in the induction head 106, therefore, it heats the part of work 116. The present invention will also work correctly with the mechanisms of other feedbacks different from those specified in the previous feedback mechanism. For example, a temperature monitor can be used in the work piece. Alternatively, other electrical characteristics (various combinations of current, voltage, power and energy) of the induction head and / or power supplies, or feedback systems described in the prior art may be used. Therefore, the present invention is contemplated to use virtually any feedback mechanism, since the precise mechanism is not important for the invention. A multi-head induction heating system made in accordance with the present invention is now shown in reference to Figure 4. The exemplary system shown is used to heal the perimeter, or perimeter portions, of a car door 411 with a plurality of induction heads 403A-403H. The induction heads 403A-403H are formed such that they align with the perimeter of the workpiece, (the gate 401 in this example). Each induction head 403A-403H is connected to the coupler of the transformer 402A-402H. Each coupler of the transformer 402A-402H is connected to the power source 405A-405H. Each power source 405A-405H includes the circuitry to receive the input power and provide an appropriate AC signal to the coupling transformer and to the head, which couples the signal to the induction head. For example, in the preferred embodiment each power source 405A-405H includes an energy inverter, a coupler and an output inverter, such as those shown in Figure 1-3. However, the invention should not be considered limited to the preferred mode and embodiment shown above, unlike this any suitable induction heat energy source will suffice. In the preferred embodiment each of the power sources 405A-405H is connected to the controller 407. The controller 407 includes a microcomputer or microprocessor and uses a program time and energy parameters for each of the 405A power sources. 405H. In the preferred embodiment, the controller 407 is used to ensure that each induction head 403A-403H is used with the appropriate amount of time and receives the appropriate amount of energy. Additionally, as shown schematically, the signals are provided from the transformer coupler to the power sources to provide the feedback as described above. Therefore, using a feedback system such as that described with reference to Figures 1 to 3, each power source can be set separately to the power that is supplied to the transformer coupler and to the respective induction head in such a way that the appropriate amount of the head is provided to the work piece 401. For example, the feedback is provided for the induction head 403A and for the transformer coupler 402A to the power source 405A. Depending on the desired energy and the feedback signal, the power source 405A adjusts the power provided to the induction head 403A such that the appropriate amount of energy is delivered to the workpiece 401. If, for example, the induction head 403B is located in the desired precise location, then the power source 405B increases the current provided to the coupler of the transformer 402B in such a way that more current is provided to the induction head 403B so as to compensate for the inappropriate position. The signal indicative of the desired value is provided by the controller 407 to the respective power sources 405A-405H. In an alternative embodiment, the controller is integrated with a power source. Also, multiple sources of energy can be networked. As can be seen, the present invention allows the healing of the entire perimeter of the work piece, but also allows the healing to be performed in segments in such a way that the energy provided to the work piece is controlled more precisely for each portion of the work piece. This numerous rule is referred to as an inductive heating system with continuous segmented perimeter. The segments generally cover the entire perimeter of the workpiece (or a continuous portion thereof), except for the gaps between the induction heads, which are smaller than the heads themselves. In the preferred embodiment the adjacent heads rest or almost rest on one another. In other embodiments the adjacent heads are superimposed. As one skilled in the art will recognize, any number of feedback systems can be used. Additionally, an open circuit system can be used. In any case, the advantage of having a segmented perimeter healing system can be beneficial to allow control of individual segments of the work piece. If a feedback system is used, it does not matter what type of feedback is used. Nor, for the preferred embodiment, does it matter which power source is used, only that the power source can be connected to the induction head (preferably but not necessarily by means of the transformer coupler).

Alternative arrangements include that the heads cover only a portion of the work piece, or have a dedicated controller for each head and power supply. In this alternative, the heads can form segments that cover all or a part of the perimeter of the work piece. Another arrangement involves using multiple heads that cover a portion or the entire perimeter of the work piece and connect the heads to the simple power supply. Another new aspect of the present invention is the use of a controller 407. In one embodiment, the controller 407 is a computer based on a microprocessor. Which has for example, an 8051 microprocessor in it. In a simple head embodiment, a microprocessor 806196KB is used. The microprocessor provides as output, the information of the energy source 403A-403H which indicates the desired heat time and the energy used for the induction heating process. The controller 407 includes, in the preferred embodiment, a program that allows registering a fault condition in the induction heating process. The 407 controller also provides additional output / input control, such as auxiliary on-off equipment. For example, a cooling pump at the end of the heating cycle can be turned on to cool the work piece, or a clamp can be activated before the heating starts.

This input / output control is particularly useful for applications other than automotive applications. The controller 407 also presents the parameters of the process in real time. For example, the frequency of the voltage current and the energy that is supplied to the work piece can be presented in real time. This is useful to turn on the system, specifically the user can add capacitance, increase the frequency, or adjust the output of the current based on the observed real-time process parameters. The controller 407 detects when a fault occurs in the process, and records the operating parameters (such as current, frequency, voltage, energy, etc.). When the heating cycle is complete, the controller 407 allows the user to access the Registered information to cause the failure and how to correct the fault. Also, the fault light illuminates (both when the fault occurs or at the end of the warm-up cycle) to notify the user that a fault has occurred. Different types of faults can be detected, and in the preferred embodiment a fault can occur when the frequency, the power consumption, the voltage, the output current, or the voltage line varies from the nominal values, or when it fails a semiconductor. For example, an over-frequency fault occurs when the frequency exceeds approximately 65 kilohertz. This condition indicates that the capacitor used to couple the impedance of the head does not have enough capacitance (or the head is shortened). The owner's manual can indicate the appropriate corrective action, such as placing a larger capacitor when the fault occurs. The correction of the failure can be more automated in alternative embodiments. For example, a controller 407 that requires corrective action in a fault check box may be included, and then indicate to the user both the failure and the corrective action. Another alternative embodiment is to have a controller 407 that sends the signals that will automatically cause the capacitor to be re-connected in an appropriate configuration. This kind of automated action can be followed or taken with other faults in the same way. Another fault that is detected is a lower frequency fault. When the frequency falls below approximately 3 kilohertz it is possible that a lot of capacitance was used or an open coil situation is present (the coil is open in the circuit). The controller 407 also controls the power consumption of the work piece. If the power consumption is less than that required (approximately 2% in the preferred embodiment) then a fault is recorded.

This failure generally indicates that the work piece is improperly positioned with respect to the head (or vise versa). The controller 407 also detects a fault when a significant voltage imbalance in the output occurs. Many power sources receive an output of 460 volts and divide it into a 230 volt output. However, in the event of the failure of a part, the conductors may be unbalanced. Therefore, controller 407 records the unbalance of the conductor and indicates the fault when the driver is unbalanced (by a conductor exceeding approximately 420 volts in the preferred embodiment). Additionally, in the preferred embodiment, controller 407 records the voltage output of the line. If the line voltage varies approximately plus or minus 20% of the nominal line voltage, the controller 407 indicates that a fault has occurred and records the operating parameters. Controller 407 also records the failure for the semiconductor. Specifically, controller 407 looks for high pulse current, such as those greater than 100 amps in the primary. This high pulse current indicates an IGBT or other breaker failure in the inverter, and controller 407 indicates a fault and records the data or information. Figure 5 is a flow chart indicating an embodiment of a program used by the controller 407 to control and record the fault information. The flow chart begins at step 501, and at step 502 it is determined if there is a fault present. The faults that are monitored can be any failure that the programmer wishes, but in the preferred embodiment are those faults that were referred to above. If no fault is present, the program recycles and re-checks for any failure. If there is a fault present, the timer starts at step 502. After the timer started, a determination is made as to whether or not the amount of time that has elapsed in step 503 was determined. In the preferred embodiment, the predetermined amount of time is a quarter of a second. In other words, a fault can exist for at least 250 milliseconds before the information is recorded and a failure is present. If the time has not elapsed, this time is increased in step 504, and in step 505 it is determined whether the fault has been resolved. If the failure has been resolved, the process is restarted by verifying a failure again in step 501. If the failure has not been rectified the time during which the fault was present is redetermined in step 503. Therefore the program Initial monitoring may or may not be the present failure and verifies the time that elapsed until the fault was resolved or until 250 milliseconds had elapsed. If 250 milliseconds have elapsed, then faults are recognized in step 504. This may include lighting a light on the front control panel. After the failure is recognized the information is recorded in step 505. In the preferred embodiment the voltage, current, frequency and energy is recorded. However, in alternative embodiments other operating parameters may be recorded. Registered information can be provided to the user on a screen by means of a printer or other output devices. Multiple fault information (for example five) can be recorded and can be provided to the user. After the information is recorded, it is determined whether the failure has been resolved in step 507. If the failure in step 507 has not been resolved, the time in step 508 is increased. Time continues to increase until the faults are resolved (as determined in step 507). Therefore, the length of time during which the fault is present is also determined. In step 509 the time of failure is recorded and the program is completed. In the preferred embodiment the program can be operated as a continuous circuit, where after the fault is resolved and time is recorded in step 509 the program starts again.

Therefore it can be seen that the present invention as described together with the controller 407 and the flow chart of Figure 5 provides a method and apparatus for controlling the condition of the induction heating process for recording information failures if Some fault occurs. Other modifications may be made in the design and arrangement of the elements discussed herein without departing from the spirit and scope of the invention, as expressed in the appended claims.

Claims (8)

1. CLAIMS 1. A system for inductive heating of a work piece comprising: a controller; a plurality of power supplies configured to receive and send signals to the controller; and a plurality of induction heads, each configured to receive the energy of one of the pluralities of the energy sources. The system according to claim 1 wherein the plurality of the induction heads are configured to be aligned with the plurality of adjacent segments of the workpiece. The system according to claim 1 wherein the plurality of the induction heads are configured to align with a plurality of segments adjacent the perimeter of the workpiece, and measure the perimeter of the workpiece. The system according to claim 1 wherein the gap between the adjacent induction heads is less than one half the size of the adjacent induction heads. 5. The system according to claim 1 in the controller and each of the plurality of energy sources include the feedback mechanisms for controlling the distribution of energy to one of the plurality of segments of the workpiece. The system according to claim 5, wherein the feedback mechanisms respond to the magnitude of the current provided for one of the pluralities of the induction heads. The system according to claim 5, wherein the feedback mechanisms respond to the energy provided. The system according to claim 1, wherein each of the plurality of the induction heads are controlled separately from the other induction heads.