KR100278581B1 - Induction Dryer And Magnetic Separator - Google Patents

Abstract

An apparatus for induction heating of the can lid 100 by winding the induction coil 223 partially or wholly around the can seal is operated at an intermediate frequency. No focusing core is required, nor is the conductor cooled with water. The can end may be conveyed through the device in the form of an in-stick 208. IGBT 230 is used within the H bridge of the inverter. The control system (Fig. 19) minimizes the peak current flowing through the switch. The control system observes the tank voltage phase angle and responds to it optimally to turn the switch on and off. The can lid 100 is magnetically separated while being guided by electromagnets that are switched sequentially. The can body may be rotated by the separate transport belt 210 while being transported. Closed-loop temperature control is provided to control the AC power input and to prevent the can seal from breaking in the event of an unplanned downtime in the manufacturing line.

Description

[Name of invention]

INDUCTION DRYER AND MAGNETIC SEPARATOR

[Technical Field]

This application is partly filed in US patent application Ser. No. 07 / 621,231, filed Jun. 30, 1990, filed Jun. 4, 1990, filed part of US patent application Ser. No. 07 / 532,945. Said patent application is incorporated herein by reference.

A method of heating or otherwise treating a metal body of the present invention, in particular by induction by drying and curing metal can lids (sealings, ends) or can bodies, maintaining the gap between them and guiding them along a path A method and apparatus for heating or otherwise treating.

[Background]

Seals for beverage containers made of metal are generally circular in shape and have flanges attached to the boundaries called curls. The base is usually made of aluminum or steel, and the curl is used to attach the seal to the can body via a seam process. In order to integrate the so formed seal between the can body and the seal, a method of applying a bead of sealant or adhesive (“composite”) into the curls has typically been done during the manufacture of the seal. Other types of coatings are optionally or generally also applied to can seals and can bodies, for example to repair damaged coatings, so that they can be used for a variety of other purposes. In this specification, the coatings, sealants and adhesives are all considered to be "liquid" applied to the workpiece.

One problem arising from this manufacturing process is that such liquids harden or dry. Recently, there has been a growing interest in the container industry for the use of water-based sealants that are dried in a state capable of applying seals to can bodies after 3-4 days. This is not a serious problem when using a solvent-based liquid because the volatile solvent dries to such an extent that the seal can be applied to the can body within 48 hours by rapid evaporation.

In the past, the can seal was heated to perform the drying and curing process by infrared radiation or convection heating. These systems, especially convection heating systems, are expensive to operate because they are large, bulky and have low energy efficiency.

Attempts have also been made to induction heating the ends of the cans. Induction heating of the conductive object is performed by passing the oscillating current through the work coil to generate an oscillating magnetic field where the conductive object is placed. Heat is generated in the workpiece as a result of eddy current losses resulting from circulating currents induced in the workpiece by the magnetic field.

1 shows an electric circuit for performing conventional induction heating. This circuit consists of a DC power supply 110 with an H bridge 130 connected between the outputs. The H bridge 130 is made up of four thyristors 112, 114, 116, 118, and a parallel resonant tank circuit 120 is connected across the H bridge in series with the current limiting inductor 122. The tank circuit 120 is composed of a work coil 124, a load represented by an equivalent resistance 126 and a capacitor 128, all of which are connected in parallel.

In steady state operation, energy is applied back and forth between the capacitor 128 and the inductor 124 so that an oscillation voltage is applied across the tank circuit 120. To compensate for energy loss through equivalent resistor 126, a control circuit (not shown) periodically operates the thyristor of the H bridge to supply additional energy into tank circuit 120. The oscillation voltage has a frequency that varies somewhat depending on the load (eg, workpiece) appearing at the heater at a given point in time, but conventional systems determine when to operate the thyristor except for the overall method applied over a long time. When did not consider this point.

The series inductor 122 is sometimes inserted into the tank circuit 120 to reduce the current peak when the thyristor is operated and to protect against large current surges in the event of a malfunction. The current through the thyristor is still huge, but water for cooling the connection line connecting the power source 110 to the H bridge 130 and the H bridge 130 to the tank circuit 120 as well as the thyristor itself. Or liquid).

A typical induction heating circuit operating at high frequencies (around 100 kHz) may use a power MOSFET as a switch in the H bridge because the MOSFET can be turned on and off very quickly. MOSFETs capable of operating at higher voltages in induction heating circuits have very high resistance, but still need to be cooled with water. Some induction heating circuits use an SCR in the H bridge, which is difficult to control even though the SCR is quickly turned on and off. A large base current amplifier is required to operate a standard bipolar transistor, and operation is not smooth at high switching speeds and high currents that the H bridge must carry in the circuit of FIG.

Conventional induction heating methods used to heat the can seal have the problem of minimizing the depth at which current is generated in the can seal by typically operating at high frequencies (around 100 kHz). This means that oscillating currents in the conductors flowing towards and into the work coils also mainly flow along the outside of the surface of these conductors ("surface effect"). Since the current density formed along the outer surface of these conductors is very high, water cooling is required by causing overheating. Typically, these conductors are configured to allow the use of copper pipes through which water flows through the center.

Since the can ends are made of steel, it is also very difficult to induction heat the can ends. Induction heating at high frequency causes a problem that heating is not performed uniformly. Different parts of the sheet metal workpiece are heated with large temperature differences depending on their proximity to the coil and other factors. Thus, even before a portion of the workpiece is heated to a predetermined temperature, local overheating occurs easily and frequently. In US Pat. No. 4,017,704 to Colin, to solve this problem, the coil can be placed flat on the transport belt and the coils can be uniformly concentrated in the open center region and can end. A method of passing a can end under a high frequency induction heating coil having a bowtie-shaped core disposed adjacent to the center and typically having a low number of turns is disclosed. This method is effective for uniformly heating the can ends, but it still requires a focusing coil, a water cooling line (copper plate) and a switch to perform such a method.

In addition to the above patents, a general induction heating apparatus is also disclosed in the following U.S. patents, although it is not the main purpose to solve any particular problem caused at the can end and can body. U.S. Patent 4,339,645 to Miller, U.S. Patent 4,481,397 to Morris, U.S. Patent 4,296,294 to Beckert, U.S. Patent 4,849,598 to Lazaki, U.S. Patent No. to Schaeffler 4,160,891, US Pat. No. 3,449,539 to Schaeffler, US Pat. No. 4,307,276 to Kurata, US Pat. No. 4,582,972 to Curtin, US Pat. No. 4,673,781 to Nouns, Camus U.S. Patent 4,531,037, U.S. Patent 4,775,772 to Shaboso, U.S. Patent 4,810,843 to Wicker and U.S. Patent 3,727,982 to Ito. Some of these disclosed systems may be used to heat can seals, but do not provide optimal results. In particular, for example, when the size and volume are very large, water cooling is necessary and heating is not performed uniformly when applied to the can ends.

Metal can ends are typically transported into the heat treatment apparatus in either of two ways. They may be transported by transport belts. In this case, the seal may be laid flat on the belt on which the coating and the composite are placed on one side, or may be laminated (“in-stick”) in the track or cage with mutual face to face contact. The previous technique is disclosed in a patent issued to Colin, and in the technique described later, the seal is pushed through the device in a direction crossing the face. To heat the can ends pushed through the in-stick, more can ends can be stacked to a predetermined track length, requiring only less floor space. However, this technique is not often used because convective air cannot directly heat the face of the can end.

Sullivan, U. S. Patent No. 4,333, 246, discloses a solution to this problem, but this also has the limitation of using the convection dryer method.

In Sullivan's patent, the workpiece is pushed through a curved path defined by a trackwork with a constant width and turning on a part of the workpiece close to a short radius, resulting in the separation of the wing shape near the long radius. . The patent uses this trackwork to partially separate the can lid when the heated air is directed towards the separation zone.

The technique used in this patent has a number of major drawbacks. Firstly, each part of the workpiece is separated from the other workpiece, but there is always another part of the workpiece in contact with the other workpiece (part close to the small radius). These parts just unfold and are not in fact separated. Thus, if the device is used to cure a liquid selectively applied to the can lid, it can only be used, for example, if the liquid is applied somewhere other than the outer periphery with which the lid is in contact with each other. In addition, since the pressure on the parts of the cover that are in contact with each other is caused by the force pushing the cover along the track, the metal part of the cover or its coating may be softened and / or damaged. And in the device, in order to achieve greater separation, the curve of the trackwork must be more strict, so that the device that pushes the cover along the track requires greater force and stronger material, so that the spread between Separation is only in a limited state. For the same reason, even if the curve remains narrow, this technique cannot be used if the transport path is very long. In addition, the technique disclosed in the above patent does not suitably apply to a can lid with a pull ring because the can lid is not well seated and scratched when contacted with each other.

Whether the can ends are transported flat or in-stick, the conveying speed and length of the drying apparatus can be discharged out whenever a sufficient amount of water or solvent in the applied liquid is discharged from the apparatus. Is chosen. However, problems arise when the manufacturing line is interrupted or shut down for some reason. In this case, the can seals in the heating device remain longer than originally intended, resulting in excessive heat and potentially breakage. In order to solve this situation, a closed loop mechanism has been provided in the past, but the mechanism only observes the air temperature in the furnace. The closed loop mechanism did not observe the temperature of the can seal. Also, for IR systems and high temperature convection systems provided with such a mechanism, it is difficult to stop the heating process quickly enough to avoid damage. There is a low temperature convection heating system that prevents overheating of the can lid by not reaching a high temperature that causes damage, but it is not desirable because of the low temperature, the drying time is long and the transportation path is long.

[Summary of invention]

It is therefore an object of the present invention to provide a can body and can seal heating device which solves some or all of the above drawbacks.

According to the invention, the coarse metal can seal is inductively heated by oscillating a magnetic field generated by an induction coil placed at an intermediate frequency and wound partially or completely several times around the can seal. By using an intermediate frequency coefficient, eddy currents develop deeply in the can ends to create a thermal energy reservoir that heats the entire workpiece more evenly. No focusing core is required and the conductors are convection cooled. Can ends may also be conveyed in-stick through the device. In addition, the reduced current allows the use of less expensive convection cooling switches within the H bridge of the inverter.

In another aspect of the present invention, a control system for a switch in an inverter for an induction heating system is provided which minimizes the peak current through the switch and eliminates the need for a series inductor conventionally used for current limiting. The control system observes the tank voltage phase angle and, in response, switches the switch on and off in an optimal state.

In another aspect of the invention, the disc shaped articles are magnetically separated while being guided by sequentially connected electromagnets.

In another aspect of the invention, the can body is rotated by a separate transport belt while being transported through the induction heating apparatus.

In another aspect of the invention, closed loop temperature control of the can seal is achieved by a device that senses the temperature of the can lid and turns off the heating means if the temperature exceeds a predetermined threshold.

[Brief Description of Drawings]

1 is a schematic diagram of a conventional induction heating circuit.

2 and 3 are side and cross-sectional views of one embodiment of the present invention.

4 and 5 are exemplary views of the induction technique according to the present invention.

6 and 7 are side views of the device according to the invention illustrating each aspect.

8 and 9 are side and cross-sectional views of yet another embodiment of the present invention.

10 and 12 are side and cross-sectional views of another embodiment of the present invention.

FIG. 11 is a perspective view of the solenoid shown in FIGS. 10 and 12.

FIG. 13 is a cross sectional view of the device of FIGS. 10 to 12 in which a small tube is used.

14 is a cross-sectional view of a modification of the apparatus of FIGS. 10 to 12.

15 is a side view of another embodiment of the present invention.

16 and 17 are side and cross-sectional views of one embodiment of the present invention for heating the can body.

18, 19 and 21 are electrical circuit diagrams for operating the induction heating apparatus according to the present invention.

FIG. 20 is a waveform diagram for explaining the operation of the circuit of FIG.

22 and 23 are side and sectional views of yet another embodiment of the present invention.

FIG. 24 is a schematic diagram of the IGBT driver board of FIG. 18. FIG.

<Description of the symbols for the main parts of the drawings>

100: can seal 202,204,206,208: guide rod

210: transportation route 220: guide

222: pancake coil 223: spiral

230: permanent magnet 240: vibrator

450: upper transport belt 452: magnetic up stacker

454: magnetic down stacker 456: lower transport belt

560: guide coil 702: transport belt

Detailed description of the invention

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings. 2 is a partially cutaway side view of an induction heating apparatus according to the present invention for heating a lid 100 made of steel (or other ferromagnetic, conductive). 3 is a cross-sectional view of the apparatus of FIG. 2. The can lid 100 has its ends placed on a pair of guide rods 202 and 204, and two other guide rods 206 and 208 are provided to serve to secure the seal in place. The four guide rods 202, 204, 206, 208 together define the transport path 210 for the column of the seal 100. Guide rods 202, 204, 206 and 208 are oriented in the axial direction at different circumferential positions along the inner surface of guide tube 220. Guide rods and guide tubes are made of nonconductive material such as ceramic or Teflon. Tube 220 is also preferably thermally insulated. The reason for this will be described in detail below. Guide rods 202, 204, 206, and 208 may be omitted in some embodiments. In this case, the function is replaced by the tube 220.

The pancake type induction coil 222 connected to the AC power source 68 is wound around the outer surface of the guide tube 220. The wiring 222 is composed of four side by side spirals 223. Each region faces on the outer periphery of tube 220 slightly less than a quarter arc and extends along the entire length of tube 220 where heating is desired. The individual spirals 223 form a pancake-shaped "lower coil" and partially wrap the transit path 210 around the outer periphery of the tube 220. As used herein, a coil may be partially wound around and partially bent on one side of the route, or partly wound around the route if it is flat, having a portion disposed on one or more sides of the route. All. The coil wiring is cooled by air, not by water, and is preferably a plurality of pillar lit wires. Litz wire has multiple thin solid core strands that are individually insulated and are useful for reducing heat loss due to surface effects when used at high frequencies. Wiring 222 may also be provided as a series of axially adjacent wiring sections where it is desirable to use for modularity or other purposes. The spiral 45 is wound to a high winding density in order to generate a strong magnetic field with minimal current. For example, a number of pillar wires are wound 45 times.

Instead of spiral 223, wiring 222 may be provided as a single wound core that wraps around tube 220. However, the magnetic force induced by this configuration tends to rotate the can lid around the diameter, making it difficult to keep the surface facing in the direction crossing the direction of the transport path. Also, such a configuration is undesirable because it tends to heat the permanent separator magnet. The reason for this will be described in detail below. Thus, a work coil wound completely around the workpiece can be used in the best condition when the can lid is conveyed in-stick. This will be described with reference to FIGS. 8 and 9.

The tube 220 is formed with holes 224 inward at various locations along its length to ventilate the can lid. Air can be circulated through these holes to be used for moisture removal, cooling or other processing. Spiral 223 is wound to avoid these holes 224. This affects the alternating magnetic induction system inside the tube in that respect, but because the wiring still extends over the entire length of the tube 220 used for induction heating, it is not so affected in the overall heating process.

The AC power source 68 is oscillated at an intermediate frequency of about 6-18 kHz in response to the resonance frequency of the loaded tank circuit. This generates an alternating eddy current that also oscillates at the same frequency within the metal can seal as the metal can seal 100 moves along the transport path 210. The intermediate frequency is used to heat the seal deep. This creates a heat energy store that will heat the seal more evenly. As is known, low frequencies induce current deep into the can seal, while currents induced at high frequencies are narrower. Most preferably, the alternating current power source 68 is several kilos in each direction to optimize the energy transfer efficiency of the different sizes, shapes, material constants and relative positions of the can seal 100 with respect to the coil 222. It must be discernible enough to follow the variation of the resonance frequency of the tank circuit by hertz.

Multiple magnetic bodies that can move freely within the magnetic field are distributed to share equally the complete magnetic field. Can lid preheaters use this technique to ensure that W.R. spaces are spaced vertically in a face-to-face relationship while hot air circulates around the lid. Use the product of Grace & Co. The cover enters the device at the top of the vertical column and is removed from the bottom. Permanent magnets placed vertically adjacent to the column resist the gravitational effects that fall on the floor and stack together by leaving the cover apart. Therefore, due to high temperatures, permanent magnets must be made of expensive magnetic materials with very high Curie temperatures. In addition, the technique has not been applied to covers that are transported horizontally or virtually horizontally in a face-to-face relationship because the covers are engaged from above due to friction with the trackwork or other devices supporting them. However, the concept can be used in the device according to the invention.

Thus, a plurality of permanent rail or channel magnets 230 are located in the gap between the four regions of the spiral 223 and are oriented in the longitudinal direction along the length of the tube 220. For simplicity of illustration, only one rail magnet 230 is shown in FIG. 2. The permanent magnet 230 changes the polarity of the magnet to N and S along the outer circumference of the tube 220 by changing its orientation. Although four permanent magnets 230 are shown in FIG. 3, the number is variable. In addition, the permanent magnets 230 may each be disposed along the length of the tube, or may be disposed in axially adjacent segments for modularity or other purposes. The apparatus of FIGS. 2 and 3 also includes a vibrator 240 (shown in FIG. 2 only) which mechanically vibrates the permanent magnet 230 in the axial direction.

In operation, when a certain number of can covers 100 are placed inside the tubes, the can covers attempt to share equally the magnetic field generated by the permanent magnets 230 along the length of the tubes. The friction is solved by the mechanical vibrator 240 which vibrates the magnetic field generated by them in the axial direction by vibrating the magnets 230. The vibration frequency should be around 60 Hz and the wavelength should be shorter than the gap between the covers. Vibration can be accomplished in other ways, for example by mounting the guide rods 202, 204, 206, 208 on the curved portions and oscillating them axially or using force oscillations inherent in the reverse electric field of the coil 222. Another approach is to provide a magnetic field that oscillates more slowly, particularly to vibrate the can lid 100 by surrounding a coil (not shown) around the tube 220. The vibration is also effective when the direction of movement intersects.

The can lid 220 is positioned inside the tube 220 and spaced apart by a magnetic field generated by the permanent magnet 230, so that an alternating frequency of intermediate frequency is provided to the wiring 222. As a result, an intermediate frequency alternating magnetic field is generated in each of the can lids inside the tube 220 to generate a eddy current, thereby heating and drying the can lids.

It can be seen that the high temperature is induced in the can lid 100 but the wiring 222 remains cold. It is not necessary to cool the guide coil rotated several times with water. Also, since the high temperature is generally limited to the lid 100 only, and since the permanent magnet 230 is actually located outside of the magnetic field generated by the spiral 223, the permanent magnet 230 is made of a high temperature curie material. Instead of expensive magnets, they may be constructed of low cost air-cooled ceramic magnets. Although the permanent magnets 230 are shown in FIGS. 2 and 3, it should also be noted that the alternating current can be maintained using alternating current or direct current electromagnets.

As long as no other force is applied, the can cover 100 in the tube 220 may be simply spaced apart to share the magnetic field generated by the permanent magnet 230. Guide force or guidance means may also be provided to move the cover in the longitudinal direction along the transport path 210. One way to apply such a force is to tilt the tube so that the inlet end is higher than the outlet end. This method uses gravity to obliquely distribute the can lid along the length of the tube so that the can lid spacing is closer when moving towards the outlet. When the cover reaches the outlet at maximum packing density, the magnetic field generated by the permanent magnets 230 is no longer strong enough to be subject to the gravity of the cover closest to the outlet falling out of the tube. Thus, in response to the desired can lid and the desired magnetic field generated by the spacing magnet, which are preferably introduced into the tube at one time, the angle of inclination is such that another lid can fall out of the outlet when one lid is introduced at the inlet of the tube. Can be determined. Thus, the cover can be transported through the induction dryer continuously as long as a method of releasing friction is provided.

The cover 100 can also be guided through the tube 220 by other means, for example by mechanically removing the cover from the outlet of the tube each time a new cover is introduced into the inlet. For example, FIG. 4 shows the top transport belt 450 for transporting the can lid 100 to a magnetic up stacker 452 that periodically adds a new can lid 100 to the inlet of the tube 220. . Each time such a new can cover is added, the magnetic down stacker 454 removes the can cover at the outlet of the tube 220 and places it on the lower transport belt 456 for further processing. Each time one cover is added to the inlet and another cover is removed from the outlet, the cover remaining inside the tube is automatically permanently repositioned in its longitudinal position to permanent magnet 230 (not shown in FIG. 4). Share the magnetic field generated by A rotating knife (not shown) may be used in place of the down stacker 454 to remove the individual can lid from the outlet end of the tube 220.

Another way to guide the can lid along the transport path 210 in the tube 220 is to move it as if it were part of a linear induction motor. When the spiral 223 is connected in three phases, for example, a three-phase AC power supply 68 is provided, and assuming that the spirals are properly spaced, one of the can lids 100 It is repeatedly drawn to the next lower spiral and removed from the previous spiral as the phase of the power supply 68 rotates. The spiral 223 may be connected to a displacement of a predetermined number of turns.

Otherwise, the guide means may be provided by adding a separate polyphase induction coil surrounding the pipe 220 to guide the cover 100 along the transport path inside the pipe 220. Three-phase (A, B, C) induction coil 260 is shown in FIG. Induction coil 560 may operate at low frequencies, for example at 60 Hz. The separate induction coil is not preferable in that it requires separate wiring, but in that the heating and induction functions are independently induced and maintained. Thus, the can lid may be continuously moved by the separate induction coil 560 even through a portion of the tube 220 where induction heating is not desirable. Such a feature is useful, for example, in a repair cord dryer in which the can lid may move through the induction heating of the tube, subsequently through the hot air absorbing part of the tube, and subsequently through the cooling part of the tube. In such a system, a portion of the tube may be wound with an induction coil 560, and only the induction of the tube may be provided with induction wiring 222 only in the heat portion.

Since the magnetic field generated by the induction wiring induces an undesirable current in the induction coil and vice versa, the induction coil should not be used in the same part of the tube 220 where induction heating takes place.

The induction technique described above may be assisted by strategic placement and orientation of the separator magnet 230 as needed. For example, FIG. 6 shows two permanent magnets 230 inclined from the tube 220 toward the exit. This reduces the separation magnetic field at the outlet end, so that the cover can be arranged at a tighter spacing towards the outlet end of the tube. This technique for controlling the density of the lid 100 at several points along the length of the tube 220 may be used for other purposes as needed. For example, this technique is useful if you want to simplify the process of removing the can lid from the outlet end of the tube.

The present invention allows significant flexibility in the design of the can lid handling apparatus. For example, the permanent magnets 230 (FIGS. 2 and 3) do not need to have a high Curie temperature, so they can be made of a flexible material. This allows the use of curved tube 220 as shown in FIG. The tube 700 shown in FIG. 7 mainly consists of a horizontal state, but is bent 90 degrees at the inlet to form a vertical conduit. The inlet of the tube 700 is disposed directly on the transport belt 702 which transports the can cover 100 in place. The can lid is individually drawn into the tube 700 by a permanent magnet 704 (only two are shown in FIG. 7) following the curved portion of the tube 700. Induction wiring 222 (FIGS. 2 and 3) may be provided over tube 700 or otherwise over a portion thereof as shown in FIG. 7. This technique effectively eliminates the need for up stackers. Similar curves at the exit of tube 700 eliminate the need for down stackers.

Since the aluminum can lid and body are not ferromagnetic materials, they cannot be magnetically spaced by the spacer magnets 230 (FIGS. 2 and 3). However, since the eddy currents induced therein are conducted by the wiring on the outside of the tube 220, the aluminum can lid is subjected to induction heating by the wiring 222. The induction feature of the present invention also applies to aluminum workpieces, since eddy currents induced in the workpieces generate magnetic fields that are repulsively determined in relation to the magnetic fields generated by the wiring 222. Thus, the workpiece and the wiring 222 form a rebound linear motor to drive the workpiece in the longitudinal direction along the inside of the tube 220. In addition, in the case of the ferromagnetic workpiece, the magnetic attraction to the spiral 223 may be too strong to eliminate the magnetic repulsive force generated. This is not the case with aluminum can covers. Thus, the aluminum workpiece is repelled inward from all sides of the tube substantially uniformly, thereby minimizing friction as the workpiece is driven in the longitudinal direction as it is pushed into the middle of the tube. This minimizes the need for vibrator 240. The aluminum workpiece can also be driven off by the multiphase linear propulsion motor 560 (FIG. 5) wound in multiple phases.

8 and 9 show a modified embodiment of the induction heating apparatus according to the present invention. The can seal is stacked face to face and is pushed in-stick through the heater in a direction crossing the major surface of the seal. The apparatus is similar to the apparatus of FIGS. 2 and 3, but without the separator magnet 230 and the working coil 222 is not only partially wound, as shown in FIG. The point is completely wound around.

FIG. 8 is a side view of the apparatus, and FIG. 9 is a sectional view taken along line 9-9 of FIG. In the apparatus, as in the case of FIG. 2, the can seal 100 in the form of a stick or column has its ends placed on a pair of guide rods 202 and 204, respectively. The other two guide rods 206 and 208 are provided to hold the seal in place. The four guide rods 202, 204, 206, 208 together define the transport path 210 through which the stick of the seal 100 is transported. The seals 100 are in contact with each other and are superimposed on one another if their shape allows contact. In this way, the entire stack of lids may be pushed along the transport path 210 by forces from the rear end of the stack.

In operation, the can seal is treated with an optional coating and is typically pushed to the rear end of the stack by magnetic wheels or other means (not shown). By effectively pushing each new can seal back to the stack, the entire stack is pushed by the width of one can seal. The hot seal is removed from the front of the stack at the same rate.

As the seal passes through the alternating magnetic field generated by the coil 222, intermediate frequency alternating current is generated in the seal so that heating occurs in the same manner as described above with respect to the apparatus of FIG. As in the apparatus of FIGS. 2 and 3, the apparatus of FIGS. 8 and 9 includes an AC power source 68, the current passing through the windings oscillating at about 6-18 KHz.

Coil 222 is wound using a pair of multiple Pilaritz wires that are wound substantially in electrical and physical parallel. By winding 2.5 times per inch, a parallel pair is wound 55 times along a 22 inch long tube 220. For can ends of either size, the inner diameter of the winding is about 3.25 inches. The coil current is more evenly distributed over the cross-sectional area of the winding in larger portions in conventional induction heating systems because of the intermediate frequency used in this system. Since the current density at any point in the cross section never becomes excessive, it is not necessary to cool with water, and convection cooling can be used instead. For a tank current of about 300 amps RMS, less than 700 watts are dissipated in this coil at about 8.5 KHZ.

10 illustrates another embodiment of the invention in which the can lids are magnetically spaced and magnetically induced along the transport path but do not generate induction heating. In this device, the can lid 100 (shown symbolically in FIG. 10) is conveyed into the inlet 1010 of the tube 1020 in a face-to-face orientation. The outlet end 1030 of the tube 1020 is shown slightly lower than the inlet end 1010 so that the can lid can easily move from the inlet to the outlet by gravity, although not necessary. Thus, the tube 1020 maintains the can lid in the form of a column and defines a transport path. A permanent separator magnet 1032 is disposed longitudinally outside the upper surface of the tube 1020, and a series of electromagnets or solenoids 1034 are longitudinally disposed along the outside of the bottom surface of the tube 1020. have.

11 shows one of the solenoids 1034 as a perspective view. The solenoid is mounted by means not shown so that it can be individually adjusted to be positioned slightly above or below the orthodontic solenoid shown in FIG.

12 is a cross-sectional view of the apparatus taken along line 12-12 of FIG. In addition to one can cover 100, permanent magnet 1032, tube 1020 and one solenoid 1034, FIG. 12 shows the mounting state of the permanent magnet 1032 and the solenoid 1034. In particular, permanent magnet 1032 is attached to frame 1210 which can slide up and down to another position within bracket 1212. Similarly, solenoid 1034 is attached to frame 1214, which can slide up and down to another position within bracket 1216. 13 shows how the adjustability of frames 1210 and 1214 can cooperate with the shape of such frames to accommodate small diameter tubes 1320 and thus small diameter can lids.

As shown in FIG. 10, a movement control circuit 1036 having a polyphase output and at least three phases A, B, and C is provided. The movement control circuit 1036 generates a three-phase pulse current for driving the coil 1034 in a sequentially interleaved manner. Phase and interleaving factors can be used in any number, but at least three phases are required to define the direction of motion.

In operation, the permanent magnet 1032 pulls the can lid 100, which is ferromagnetic, so that its edge contacts the inside of the upper surface of the tube 1020. Permanent magnet 1032 also has the same separation effect as previously described, but the lid 100 is mostly the edge and tube 1020 of the can lid 100 when the end is introduced into the inlet and the other part is controlled at the outlet. Because of the frictional force between the inside of the upper surface of), it cannot move in the axial direction. The solenoid 1034 instantly pulls the can lid 1020 apart from the inside of the upper surface of the tube 1020 whenever a pulse from the movement control circuit 1036 is applied to any of the solenoids 1034. This promotes the magnetic spacing generated by the permanent magnet 1032. In addition, since the solenoid 1034 is supplied with a current in a multiphase interleaved manner, the can lid 100 gradually moves toward the outlet 1030 along the transport path. The pulse frequency of the movement control circuit 1036 lies at about 20-250 Hz. Generally, the higher this frequency up to this point, the faster the can lid 100 is directed towards the outlet 1030. In addition, where it is desirable to induce heating of the can lid 100 while being guided by the solenoid 1034, the pulses provided to the solenoid 1034 may each consist of an intermediate frequency burst rather than a single cutting waveform. Otherwise, both ends of the pancake-shaped coil 1220 as shown in FIG. 12 may be attached to the outside of the tube 1020. This coil, as described above, is partially wound around the can lid 100 and may be supplied with the same intermediate frequency current described above.

Another variant is shown in FIG. 14 in which solenoid 1034 is replaced with pancake coil 1420 that is substantially completely wound around the outer periphery of tube 1020. In particular, the pancake coil is opposed to both sides 1422 and 1424 and bottom 1426 of the transport belt. The coil 1420 may be divided into a plurality of pancake-type subcoils whose edges are adjacently wound around the perimeter of the tube 1020 as needed. In addition, other coils of these coils 1420 may be wound around a longitudinally adjacent portion of the tube 1020 in the same interleaved manner as the solenoid 1034, and may be supplied with an intermediate frequency burst in a polyphase state. . In this way, the pancake-type coil 1420 assists in forming the gap by pulling the can lid 100 from the inner upper surface of the tube 1020, inducing the lid toward the outlet 1030, and simultaneously induction heating the can lid. .

15 shows an overall system for drying a liquid applied to can lid 100. The lid is pushed into the inlet of the heating zone 1512, for example 32 inches long. In the heating zone 1512, the lid is induction heated to the state of the in-stick using the principles described in connection with FIGS. 8 and 9. The heating zone 1512 may also include an IR sensor 1530. This will be described below.

The cover then enters the temperature holding zone 1514, where the covers are magnetically spaced apart using the principle to be described in relation to FIGS. 10, 11 and 12, and the outlet 1516 of the device. Magnetically induced towards The shroud is not induction heated in the temperature holding zone 1514, but instead the air circulates between the shrouds in a manner to be described later. However, because the induction heating generated while the lid was in the heating zone 1512 was achieved at an intermediate frequency to create a reservoir of thermal energy throughout the can lid, the lid was still hot when introduced into the temperature holding zone 1514. The state is maintained at a high temperature in the temperature holding area 1514. The temperature holding area 1514 is 48 inches in length, for example.

After exiting the temperature holding zone 1514, the lid magnetically separates and exits the outlet 1516 using the principles described in relation to FIGS. 10, 11, and 12 as the temperature holding zone 1514. Enters the cooling zone 1518 to magnetically guide the lid toward the side.

Arrow 1520 shows the direction of air flow in the apparatus of FIG. 15. Blower 1522 blows air at room temperature from the vicinity of outlet 1516 into a tube in cooling zone 1518. Air flows toward the temperature holding zone 1514, which then simultaneously cools the lid in the cooling zone 1518 and extracts heat for use in the temperature holding zone 1514. Once introduced into the temperature holding zone 1514, air enters the heat exchanger 1528 through a tube containing a can lid and is heated by a resistance heater 1524 and the temperature holding zone near the inlet of that zone ( 1514). The hot air then flows through the tube containing the can lid and into the temperature holding zone 1514 in the same direction as the lid is moving. Here, air removes moisture released from the can lid. Then, air flows out of the discharge pipe 1526 from a point near the lower end of the temperature holding zone 1514. A heat exchanger 1528 may be provided to connect heat from the discharge tube 1526 to air flowing through the resistance heater 1524 to conserve energy.

As mentioned above, the problem with conventional can seal drying apparatus is that the can seal in the heater tends to overheat or be damaged if the manufacturing line is blocked or interrupted for some reason. Even if a means is provided for turning off the heater when the line is interrupted, heating can continue for a very long time.

In accordance with one aspect of the present invention, a closed loop temperature control is provided that directly observes the temperature of the can lid 100. In particular, as shown in Figure 15, the temperature sensor 1530 consisting of a conventional IR sensor is disposed adjacent to the transport path in the heating zone 1512 to sense the temperature of the seal 100. If the temperature of the seal 100 is higher than the preset temperature, the IR sensor immediately detects this condition, and the AC power supply (not shown in FIG. 15) is automatically turned off. This shuts off all current flowing through the can seal, preventing the seal from becoming hot almost immediately. The quick response of the IR sensor, which detects the cover rather than the surrounding air, is combined with the quick off capability of the induction heater to prevent further heating.

The temperature sensing of the cover can also be used as part of closed loop temperature control when the induction heater performs normal operation even in the absence of failures such as line breaks. For example, it is known that when the lid 100 reaches a temperature of 150-220 ° F., the specific water-based sealant placed on the curl of the lid is efficiently heated to reach 98% solids within 10 minutes. have. Thus, a closed loop temperature sensing system for observing the temperature of the lid 100 is mounted in the induction dryer to turn off the AC power when each seal reaches a critical temperature. In this way, it is possible to accommodate seals of different sizes, thicknesses, positions or orientations without changing the configuration of the induction drying portion of the production line.

Thus far, the present invention has exemplified embodiments in which can covers are provided in a face-to-face relationship. 22 and 23 show an example of an apparatus used with the can lid of the present invention provided in a flat state on the platform. FIG. 22 is a side view of the apparatus, and FIG. 23 is a sectional view taken along the line 23-23 of FIG. The apparatus consists of a platform 2210 in which the can end 100 slides along the transport path and in the direction indicated by arrow 2212. A support 2214 having a coil 2216 at its upper surface is mounted underneath platform 2210. The coil 2216 is a spiral winding faced with the transport belt 2212 and is sequentially arranged along the transport belt. Spiral 2216 are interconnected in a polyphase manner. In particular, three spirals are connected together. Three phase AC power supplies (not shown in FIGS. 22 and 23) are respectively connected to the three phases A, B and C of the spiral. As with the other embodiments described above, the embodiments of FIGS. 22 and 23 generate high frequencies that oscillate eddy currents in the metal can seal 100 when moving along the transport path 2212. With the use of the multiphase spirals shown in FIGS. 22 and 23, single phase arrangements are provided where induction is adequately provided in other cases as described in more detail, and when induction is provided by other means, such as a mobile transport belt. to be.

16 and 17 show how the present invention is used to heat the can body. FIG. 16 is a side view of the device, and FIG. 17 is a sectional view taken along arrows 17-17. In FIG. 16, a series of can bodies 1610 is transported on a transport belt 1612 and introduced into a tunnel 1614 having both ends (only one of these 1616 is shown in FIG. 16). The pancake coil 1620 is wound at both ends and top of the tunnel, and thus is partially wound around the transport path of the can body 1610. The spiral may be connected together in series or in parallel, or a combination of both states. The device also includes fastening means shown symbolically only as 1622. The purpose of the fixing means will be described in detail below.

As shown in FIG. 17, the transport belt 1612 is substantially divided into two parts 1710 and 1712 in the longitudinal direction. The fastening means 1622 may also be divided into two parts 1714 and 1716 along the longitudinal direction. The fixing means 1622 attract the can body 1610 and are in frictional contact with both portions 1710 and 1712 of the transport belt 1612. The securing means is based on a vacuum, and when the can body 1610 is at least partially made of ferromagnetic material, the securing means is a permanent magnet or an electromagnet. The two parts 1710 and 1712 of the transport belt 1612 travel at different speeds such that the can body rotates as it passes through the tunnel 1614. Thereby, heating becomes more even.

18 shows the main part of the electronic circuit for driving the above-described coil. In FIG. 18, the tank circuit 1816 is comprised of the work coil 1810 and the parallel capacitor 1812. In FIG. The capacitor 1812 is chosen such that the tank circuit can have a resonance frequency on the order of 6-18 KHz when used with a typical workpiece in place. The capacitor 1812 is physically located close to the work coil 1810. A voltage extraction transformer 1814 with a primary coupled across the work coil 1810 is also located near the work coil 1810. In use, the tank circuit of FIG. 18 may have a 400 volt RMS voltage, for example.

The tank circuit 1816 is driven by a pump circuit including a three-phase bridge rectifier 1818 connected to the H bridge 1820. H bridge 1820 includes four NPN IGBTs 1822, 1824, 1826, 1828, respectively, driven by IGBT drivers 1830, 1832, 1834, 1836. IGBTs 1822, 1824, 1826, and 1828 each have a diode having an anode connected to the emitter of the IGBT and a cathode connected to the collector of the IGBT. The IGBT / diode combination is available in a single package, for example MG400Q1US1 manufactured by Toshiba Electronics Europe GmbH, Irvine, California. The collector and emitter of the IGBT are often referred to as the current path terminal of the IGBT, and the base is referred to as the control terminal. In the H bridge 1820, the positive output of the bridge rectifier 1818 is connected to the collectors of the IGBTs 1822 and 1826, and the negative output of the bridge rectifier 1818 is connected to the emitters of the IGBTs 1824 and 1828. Connected. The emitter of IGBT 1822 is connected to the collector of IGBT 1824 and the emitter of IGBT 1826 is connected to the collector of IGBT 1828. Filter capacitor 1838 is connected across the H bridge. That is, from the emitter of the IGBT 1822 to the emitter of the IGBT 1826. The two terminals of the capacitor 1838 are also connected side by side to the two terminals of the tank circuit 1816. A 24 volt DC power source 1939 is also connected to the collectors of the IGBTs 1822 and 1826 via the diode 1840.

Overall control of the system is performed by the microcomputer 1882. Among many other challenges, microcomputer 1882 receives sensor inputs from induction furnaces indicating the temperature of work coil 1810, receives infrared (IR) temperature readings described above with respect to 15th degree, and can end Receive an indication of whether or not it moves as expected. As can be seen, these sensing inputs cause the microcomputer 1842 to stop the operation of the device if a malfunction occurs. The microcomputer 1842 generates an operation stop signal shown symbolically as line 1844, for example, for operating the delay control of the AC power supply to the bridge rectifier 1818 connected to the crowbar circuit.

The apparatus of FIG. 18 also includes a pump controller 1846 for observing and adjusting the pump current provided through the H bridge in pulse units. To accomplish this, the pump controller 1846 receives the secondary of the voltage extraction transformer 1814 as an input and generates two control signals on lines 1848 and 1850 to control the IGBTs in the H bridge 1820. In particular, the control line 1848 is connected to the inputs of the IGBT drivers 1830 and 1836 and the control line 1850 is connected to the inputs of the IGBT drivers 1834 and 1832. The pump controller 1846 also directly observes the pump current provided via the IGBT and across the H bridge via the current extraction coil 1852 connected to the pump controller 1846. Pump controller 1846 may provide a shutdown signal to microcomputer 1842 via line 1854.

When the apparatus of FIG. 18 is first activated, pump controller 1846 provides a signal to microcomputer 1842 via line 1854 to temporarily turn off the main power source of the pump circuit. During this time, the pump circuit is supplied with a power source 1839 adjusted to 24 volts. As a result, the tank circuit 1816 can reach a steady state oscillation state before the main power is turned on. After a predetermined time has elapsed, for example, after 5-10 seconds have elapsed, if everything seems to be operating correctly, pump controller 1846 is currently powered on to microcomputer 1842 via line 1854. on) This automatically shifts the diode 1840 back to separate the 24 volt regulated power source 1839 from the system.

The pump controller 1846 observes the voltage across the tank circuit 1816 through the extraction transformer 1814 and determines the IGBT of the H bridge only when optimally determined to minimize the peak current that must flow through the IGBT. Induce. Pump controller 1846 achieves this in response to the phase of the voltage across tank circuit 1816. There is no series inductor at all between the bridge rectifier 1818 and the tank circuit 1816 of the main power supply. Phase response control of the IGBT in the H bridge is one way in which the device is protected against overcurrent, and another is to directly observe the instantaneous current passing through the IGBT via the extraction coil 1852 by the pump controller 1846. . If the current through the IGBT exceeds the predetermined threshold at any time, the pump controller 1846 stops operation of the device to prevent damage. In addition, since the apparatus heats the workpiece by induction heating rather than by infrared radiation or hot convection, the operation of the apparatus can be stopped almost immediately.

19 is a block diagram of the H bridge control of the pump controller 1846. The secondary portion of the extraction transformer 1814 (FIG. 18) is connected across the input terminals 1910, 1912 of the pulse shaper 1914. The pulse shaper 1914 actually converts the sinusoidal input voltage into a square wave and provides a signal through the line 1916 to the signal input of the phase lock loop (PLL) 1918. PLL 1918 may be, for example, Model 4046 manufactured by National Semiconductor Corporation. PLL 1918 indicates when phase lock is achieved by driving signal line 1920 low to provide an active high phase error signal to signal line 1920. The phase error signal 1920 is used as described below.

VCO capacitor 1922 is connected across PLL 1918 DML VCO C- and C + pins, which are also connected to the unconverted inputs of each follower 1924, 1926. The inverse transform input of the follower 1924 is connected to its output, and the output is also connected via a resistor 1928 to the unconverted input of the comparator 1930, and through the resistor 1932 an unconverted input of the comparator 1934. Is connected to the input. The inverting input of the follower 1926 is connected to its output, and the output is also connected to the unconverted input of the comparator 1938 via a resistor 1936 and the unconverted input of the comparator 1942 via a resistor 1940. Is connected to. The output of comparator 1930 is connected to the unconverted input through a resistor 1944. Similarly, the output of comparator 1938 is connected to the unchanged input via resistor 1946, the output of comparator 1934 is connected to the unconverted input through resistor 1948, and comparator 1942 is output. Is connected to the unconverted input via a resistor 1950. The inverse transform inputs of each comparator 1930 and 1938 are connected together to a common portion of the potentiometer 1952. The potentiometer is connected across the VCC and ground plane. Similarly, the inverse transform inputs of each comparator 1934 and 1942 are coupled together to a common portion of potentiometer 1954. The potentiometer is connected across the VCC and ground plane.

The output of the comparator 1930 is connected to the input of the one shot 1956. The output of the one shot is connected to the preset input of the D flip flop 1958. The output of comparator 1938 is connected to the input of one shot 1960. The output of the one shot is connected to the preset input of the D flip-flop 1962, and the output of the comparator 1942 is connected to the clear input of the flip-flop 1962. The output of comparator 1934 is connected to the clear input of flip-flop 1958. One shots 1956 and 1960 may be, for example, 4538 monostable multivibrators manufactured by National Semiconductor Corporation, and flip-flops 1958 and 1962 may be 4013 products manufactured by National Semiconductor. D flip-flops 1958 and 1962 may be replaced with other types of flip-flops, such as set / preset flip-flops, if desired.

The Q output of flip-flop 1958 is connected to the base of transistor 1964 and its collector is connected to VCC. The Q output of flip-flop 1962 is connected to the base of transistor 1966 and its collector is connected to VCC. The transistors 1964 and 1966 are all NPN transistors. The emitter of transistor 1964 is grounded through a resistor divider made of resistors 1968, 1970 and the emitter of transistor 1966 is grounded through a resistor divider made of resistors 1972, 1974. The connection between resistors 1968, 1970 forms a control signal 1848 (FIG. 18), and the connection between resistors 1972, 1974 forms a control signal 1850 (FIG. 18). The control signals 1848 and 1850 are both connected to the anodes of the diodes 1976 and 1978 and the cathodes of the diodes together to the terminal 1980. As will be described in more detail below, the safety circuit in the pump controller 1946 immediately stops the drivers of the four IGBTs in the H bridge by pulling the terminal 1980 low.

The operation of the H bridge control circuit of FIG. 19 can be more clearly understood through the waveform diagram of FIG. 20. In FIG. 20, waveform 2010 shows a voltage waveform across tank circuit 1816. FIG. The voltage is a sine wave with alternating opposing voltage ends with zero voltages between each pair of ends. This waveform is extracted by transformer 1814 and provided to pulse shaper 1914 (FIG. 19) which generates a square wave, shown as waveform 2012 shown in FIG. 20, via line 1916. FIG. . Waveform 2012 has the same phase as waveform 2010, and edge transitions occur simultaneously when waveform 2010 goes to zero.

Waveform 2014 represents the C + output of PLL 1918. Waveform 2014 is made of a positive ramp when the tank voltage is above zero and transitions to a flat zero voltage when the tank voltage goes below zero. Similarly, waveform 2016 represents the voltage at the C- output of PLL 1918. Waveform 2016 has a positive ramp when the tank voltage goes below zero and transitions to zero voltage when the tank voltage goes above zero. These waveforms 2014, 2016 need not be complete ramps, but should be monotonous for this circuit in the time period shown.

Waveform 2018 represents the output of comparator 1930. This device compares the instantaneous voltage of the lamp output of C- with the threshold voltage set manually by potentiometer 1952. When the C lamp voltage exceeds the threshold voltage, the output of the comparator 1930 is high. When the C- ramp voltage transitions to zero, the output of comparator 1930 also transitions to zero. Thus, the output of the comparator 1930 is preset using the potentiometer 1952 so that the rising edge is generated when the tank voltage reaches the preset phase of the cycle and the falling edge is on subsequent zero crossings of the tank voltage. A series of pulses that occur.

The output of the comparator 1930 is provided to the input of the one shot 1956, and the output of the one shot is represented by the waveform 2020. One shot 1956 only generates a short amount of spike at the rising edge of each pulse of waveform 2018.

The C- ramp signal is also provided to a comparator 1934 whose output is represented by waveform 2022 of FIG. 20. Like comparator 1930, comparator 1934 compares the ramp voltage with a threshold voltage that can be preset through potentiometer 1954 and ensures that it is only output high when the ramp voltage exceeds the preset threshold. The output of comparator 1934 is lowered again when the C- ramp voltage transitions to zero voltage. Thus, the output of comparator 1934 can be set manually so that rising edges can be generated in a phase that can be preset in a tank voltage cycle, and a series of pulses in which falling edges are generated when the tank voltage falls below zero. to be. In the comparators 1930 and 1934, it should be noted that the setting of the potentiometers 1952 and 1954 may represent a phase within the first half of each cycle of tank voltage, i.e. while the tank voltage is in a positive state. For reasons of clarity, potentiometer 1952 should be set to indicate phase at the first 90 ° of the tank voltage cycle, and potentiometer 1954 should be set to indicate phase at the second 90 ° of the tank voltage cycle.

The outputs of the one shot 1956 and the comparator 1934 are provided to the preset and clear inputs of the flip-flop 1958, respectively. Thus, as represented by waveform 2024, flip-flop 1958 starts on the Q output at the phase of the tank voltage indicated by potentiometer 1952 and ends at the phase of the tank voltage indicated by potentiometer 1954. Generate a waveform with positive pulses.

Since the output of the flip-flop 1962 is generated in a similar manner to the flip-flop 1958, a description thereof will be omitted. However, it is evident that the output of flip-flop 1962 will have a waveform similar to waveform 2024 (FIG. 20) except that the tank voltage is shifted 180 °. This is shown as waveform 2026 superimposed on waveform 2024 for clarity of illustration. The start of each pulse in the form of waveform 2026 is set by the same potentiometer 1952 that sets each start of the form in waveform 2024, and the start of each pulse in the form of waveform 2024 is defined by the respective tank. The same waveform as that shown in the positive half of the voltage cycle is shown in the negative half of the tank voltage cycle. Similarly, the end of each pulse of waveform 2026 occurs in response to the same threshold setting of potentiometer 1954 that determines the end of each pulse in the form of waveform 2024. The end of each pulse in the form of waveform 2026 is generated in the same phase at the negative half of the tank voltage cycle in which the end of each pulse in the form of waveform 2024 is generated in the positive half of each tank voltage cycle. .

The Q output of flip-flop 1958 is provided to driver boards 1830 and 1836 of H bridge 1820 (FIG. 18) via drive circuit or control line 1848. Accordingly, the IGBTs 1822 and 1828 are turned on to conduct current into the tank circuit 1816 only while the pulse of the waveform 2024 is high. Similarly, the output of flip-flop 1962 is provided to IGBT drivers 1834 and 1832 via drive circuit and control line 1850. Accordingly, the corresponding IGBTs 1826 and 1824 are turned on to conduct current into the tank circuit 1816 only while the pulse of waveform 2026 is high. The current in the latter flows through the tank circuit 1816 in the opposite direction to the former case.

In order to minimize wear and tear on the IGBTs within the H bridge, it is desirable to set potentiometers 1952, 1954 to minimize the peak current that must flow through such IGBTs. Thus, the time of each cycle when the voltage across the tank circuit 1816 is at its maximum is preferably included in the period in which the IGBTs 1822 and 1828 are enabled. At that time, the voltage drop from the collector to the emitter of the IGBT 1822 is minimized, thereby minimizing the flow of current through it. Similarly, the voltage drop between the collector and emitter of IGBT 1828 is also minimized at this time, thereby minimizing the current flowing through IGBT 1828. Thus, the time period in which IGBTs 1822 and 1828 are enabled must be set via potentiometers 1954 and 1954 to start and end at an appropriate phase angle before and after the voltage maximum of each cycle of tank circuit 1816. Similarly, to minimize the peak current flowing through IGBTs 1826 and 1824 for the same reason, potentiometers 1952 and 1954 set these IGBTs so that an appropriate time period is set near the voltage minimum of the waveform on tank circuit 1816. Must be set to enable.

Waveform 2028 (FIG. 20) is formed across the H bridge when potentiometers 1952, 1954 are set to enable the IGBT immediately before each peak voltage and to disable the IGBT immediately after each peak voltage. The current waveform is shown. As shown, the waveform consists of an alternating series of positive and negative pulses, whose active period begins by rising to the maximum and at the same time sinks to the minimum when the tank voltage waveform reaches the extreme and is blocked at the end of the pulse. Until it rises again. Applicants have found that the peak current through the IGBT is minimized when potentiometers 1952, 1954 are adjusted such that each pulse is blocked when the magnitude of the current once again reaches the maximum achieved during the first portion of the pulse. In a variant embodiment, an H bridge control circuit is provided which automatically extracts and maintains the peak value at the first portion of the pulse and terminates the pulse when the peak value is once again achieved.

As noted above, the pump controller 1846 (FIG. 18) also includes a safety feature that protects against unwanted current surges that have been avoided by a series inductor as shown in FIG. 21 shows a circuit for realizing some of these safety features.

In FIG. 21, current extraction coil 1852 is connected to two inputs of differential signal regulator 2102. In FIG. The signal conditioner 2102 mainly filters noise from the extracted signal and places it within the normal range. The output of differential signal regulator 2102 is connected to the inverse transform input of comparator 2104. The output of the comparator is connected via the resistor 2106 to the unconverted input of the comparator 2104. The unconverted input of comparator 2104 is also connected to a connection point of resistor divider 2110 connected between VCC and ground plane via resistor 2108. The output of the differential signal regulator 2102 is also connected to the unconverted input of another comparator 2114 via a resistor 2112. The output of the comparator is connected to the unconverted input through a resistor 2116. The inverse transform input of comparator 2114 is connected to the junction of resistor divider 2118 connected between ground plane and VEE. In this circuit, VCC is +15 volts and VEE is -15 volts. The output of comparator 2104 is connected to the cathode of diode 2120. The anode of the diode is connected to the connection node 2122. Similarly, the output of comparator 2114 is connected to the cathode of diode 2124, and the anode of the diode is connected to node 2122.

The phase error signal 1920 from the PLL 1918 (FIG. 19) is connected to the inverting input of another comparator 2128 via an analog switch 2126 and grounded through a resistor 2130. The output of comparator 2128 is connected to a non-converting input via resistor 2132 and to the connection point of resistor divider 2134 connected between VCC and ground plane. The output of comparator 2128 is connected to the cathode of diode 2136 and the anode of diode is connected to node 2122.

Node 2122 is connected to VCC through resistor 2138 and to base of transistor 2142 through resistor 2140. The base of transistor 2142 is also connected to the cathode of diode 2144 and the anode of the diode is grounded. The emitter of transistor 2142 is grounded, the collector is connected to VCC through pull-up resistor 2146 and also to the clear input of D flip-flop 2148.

Also provided is a comparator 2150 where the inverted input is grounded and the unconverted input is connected to the junction between VCC at capacitor 2152 and VEE at resistor 2154. Capacitor 2152, resistor 2154 and comparator 2150 cooperate to provide a power on time delay of about 5-10 seconds. The output of comparator 2150 is connected to the anode of diode 2156 and is connected to VCC through resistor 2158. The cathode of diode 2156 is grounded through resistor 2160 and is also connected to the preset input of D flip-flop 2148. The cathode of diode 2156 is also connected to the control input of analog switch 2126.

The Q output of flip-flop 2148 is connected to the base of transistor 2164 through resistor 2162 and also to the base of transistor 2168 through resistor 2166. Emitters of transistors 2164 and 2168 are grounded. The collector of transistor 2164 is raised to VCC by pull-up resistor 2170 and is also connected to the base of another transistor 2174 through resistor 2172. The emitter of transistor 2174 is grounded and the collector is shutoff line 1980 shown in FIG. The collector of transistor 2168 is connected to the cathode of the LED in optoisolator 2184 via analog switch 2182, and the anode is connected to VCC through resistor 2186. The control input to analog switch 2182 is connected to the cathode of diode 2156. The collector of the NPN output transistor of the opto-isolator 2184 is connected to the base of the PNP transistor 2188 and the emitter is connected to VCC. An emitter of the output transistor of the optical isolator 2184 is connected to the collector of the transistor 2188 and also forms a stop signal 1854 provided to the microcomputer 1842 (FIG. 18). Analog switches 2126 and 2182 may be realized in a 4016 chip manufactured by National Semiconductor Corporation, and are also connected to close when the control signal is low and open when the control signal is high.

In operation, increasing the energy consumption, comparator 2150 provides a high output signal for 5-10 seconds, after which a low output signal. This isolates the stop signal 1980 by presetting flip-flop 2148. As discussed above in relation to FIG. 19, the low voltage on line 1980 keeps all IGBTs in the H bridge off, but when the line 1980 is disconnected, the IGBTs operate normally. In addition, during the time when the energy consumption increases, the control input to the analog switch 2182 is high, so that the switch is opened and the transistor 2188 is turned off. Signal 1854 entering microcomputer 1842 is lowered by a pull down resistor (not shown) in microcomputer 1842. Analog switch 2126 is also open at this time and lowered by resistor 2130. The output of comparator 2128 is thus high, and diode 2126 is reversed. Therefore, the phase error signal 1920 does not have any influence on the node 2114 at this time. The output of the comparators 2104 and 2114 can also be estimated to be high at this time, whereby the diodes 2120 and 2124 are shifted in reverse. Thereby, the node 2122 is raised by the resistor 2138 so that a non-active value (low value) is provided to the clear input of the flip-flop 2148. However, even if an active value (high value) is provided to the clear input of flip-flop 2148 at this time, it does not affect as long as the preset input remains high.

After the capacitor 2152 is sufficiently charged, the comparator 2150 outputs a drop to a low voltage. In combination with the pull-down resistor 2160, the cathode of the diode 2156 is lowered so that the analog switches 2126, 2182 are conductive. This also terminates the presetting of flip-flop 2148. Unless immediately erased, the Q output of flip-flop 2148 will remain high to challenge transistor 2168. This activates the LEDs in the isolator 2184 and pulls the line 1854 high and sends a signal to the microcomputer 1842 to turn on the main power.

During normal operation, the circuit of FIG. 21 constantly observes the current being passed through the IGBT of the H bridge 1820 and pumped into the tank circuit 1816 through the current extractor 1852. As long as the instantaneous current does not exceed the maximum threshold set by the resistor divider 2110, the comparator 2104 pulls the node 2122 low to turn off the transistor 2104 and turn off the clear input of the flip-flop 2148. Activate it. Similarly, comparator 2114 activates clear input of flip-flop 2148 by pulling node 2122 low, unless the instantaneous current falls below the negative threshold set by resistor divider 2118. do. Also, unless the phase lock loop 1918 (FIG. 19) detects a phase error, the phase error line 1920 is activated so that the node 2122 is pulled low and the clear input of the flip-flop 2148 is activated. do.

When flip-flop 2148 is erased, transistors 2168 and 2164 are both off. This causes the signal on line 1854 to be pulled low by the pull-down resistor in microcomputer 1842 and to actively pull the signal on line 1980. The low value on line 1854 signals the microcomputer to stop the system, and the low voltage on line 1980 immediately stops the IGBT in the H bridge 1820, as mentioned above. In this way, the system is protected from overcurrent passing through the H bridge 1820 without requiring series inductance.

FIG. 24 schematically shows one of the IGBT driver boards 1830 shown in FIG. The remaining driver boards 1832, 1834, 1836 are identical. The driver 1830 consists of an optical isolator 2410 having paired input lines connected to a control signal line 1848 (FIG. 18) and a ground plane on the pump controller 1846, respectively. The output side of the optoisolator 2410 is connected to a +/- 15 volt output of a separate onboard power source (not shown) and provides an output signal via line 2412. Line 2412 is connected to the base of NPN transistor 2416 through resistor 2414, and the collector of the transistor is connected to a +15 volt power source. The base of transistor 2416 is also connected to the base of PNP transistor 2418, and the collector of the PNP transistor is connected to the emitter of transistor 2416. The emitter of transistor 2418 is connected to a -15 volt power source. The junction between the emitter of transistor 2416 and the collector of transistor 2418 is connected to the base (FIG. 18) of IGBT 1822 via resistor 2420. The base of the IGBT 1822 is also grounded via 15 volt Zener diodes 2422 that are oriented in opposite directions and connected in series. The emitter of IGBT 1822 is also grounded. The collector of IGBT 1822 is connected to a cathode of a 100 volt zener diode 2426 via a resistor 2424, the anode of which is connected to the base of another NPN transistor 2428. The emitter of transistor 2428 is connected to a -15 volt power supply via resistor 2430 and also to the base of NPN transistor 2432. Collectors of transistors 2428 and 2432 are coupled together to the base of transistors 2416 and 2418.

In normal operation, the pulse received on line 1848 is transmitted by line isolator 2410 as positive pulse through line 2412. The signal is buffered by transistors 2416 and 2418 to provide a positive pulse on the baseline of IGBT 1822. Zener diode 2422 provides extra protection by preventing the base lead from exceeding + or-15 volts. In addition, when the collector of IGBT 1822 exceeds 85 volts, zener diodes 2426 are destroyed and transistors 2428 and 2432 pull the bases of transistors 2416 and 2418 down close to -15 volts. This extra protection keeps the base drive current of the IGBT 1822 off when the voltage across the IGBT exceeds about 85 volts, regardless of the signal arriving through line 1848.

Since the induction heating system has a very high electric noise, in addition to the above-mentioned, general care is required in the design of the electronic control circuit for controlling such noise. For example, shielded and twisted pair wiring should be used whenever possible.

Using the apparatus and method described above, the efficiency of the actual system is limited to about 70-80%, while achieving efficiency of 90% or more (as the ratio of energy entering the AC power source to the AC power source). can do. This compares with the conventional efficiency level which is always below 70%.

Although the present invention has been described in connection with specific embodiments as described above, many modifications are possible without departing from the scope thereof. For example, the present invention is not limited to metal can seals, but may be used with an electrically conductive workpiece in a flat form, preferably but not necessarily. As another example, a single phase pump circuit may be used instead of the above-described abnormal pump circuit. Similarly, connections with other types of tank circuits besides H bridges may be used, and other types of switches may be used instead of IGBTs, if the defects can be tolerated. As another example, when the above-described circuit observes the current or the voltage for various purposes, the circuit may be appropriately modified to observe the voltage and the current. In addition, although the pancake coil is wound around the transport path as much as possible, the advantages of the present invention are obtained even when the coil is wound to a greater extent than a flat coil mounted only on one side of the workpiece as in the conventional case. can do. The more complete the winding, the better, but it may be wound about 3/4 or 2/3. Various other modifications can be implemented.

Claims (26)

A transport path through which the workpiece moves in the longitudinal direction, wherein the transport path has a longitudinal segment; A non-liquid cooling induction coil at least partially surrounding the longitudinal segment of the transport path; And a predetermined frequency oscillation current source for oscillating an electric current and causing the current to flow in the induction coil. 2. The apparatus of claim 1, wherein the induction coil comprises at least one wire that completely surrounds a longitudinal segment of the transport path. The apparatus of claim 1, wherein the induction coil comprises a pancake-type coil wound at least partially around a longitudinal segment of the transport path. The electrically conductive workpiece heating device of claim 1, wherein the electrically conductive workpiece heating device is configured to heat the plurality of electrically conductive workpieces, which are moved in-stick along the transport path and are in contact with each other. The electrically conductive workpiece heating apparatus of claim 1, wherein the current oscillates at a frequency between about 6 kHz and 18 kHz. The electrically conductive workpiece heating apparatus according to claim 1, wherein the induction coil is air cooled. 2. The apparatus of claim 1, wherein the predetermined frequency oscillating current source for oscillating an electrical current comprises power supply means for generating a current having an oscillation frequency in the induction coil having a varying oscillation frequency to optimize energy transfer efficiency to the workpiece. An electrically conductive workpiece heater, characterized in that. 2. An electrically conductive workpiece heating apparatus according to claim 1, wherein the workpiece has a non-coagulating coating and the coating solidifies by heating. 2. The work piece of claim 1 wherein the workpiece is one of a plurality of electrically conductive can ends, and the heating device further comprises magnetic means for generating a magnetic field effective to separate the can ends to share the magnetic field. Electrically conductive workpiece heater. An apparatus for carrying a plurality of can ends, comprising: support means for supporting the can ends in a substantially horizontal row; Can end conveying device comprising a magnetic means effective for generating a magnetic field and separating the can end to share the magnetic field. 11. The can end transport apparatus according to claim 10, wherein the magnetic means is maintained in a face-to-face relation with the can end separated. 12. The can end transport apparatus according to claim 11, wherein said magnetic means is comprised of channel magnets extending longitudinally along said row. 11. The can end transport apparatus of claim 10, wherein said magnetic field varies gradually longitudinally along said row. 11. The can end conveying device of claim 10, further comprising motivating means for guiding the can end along the heat. 15. The method of claim 14, wherein the row has an inlet end and an outlet end, wherein the inducing means comprises means for adding the can end to the inlet end of the row and means for removing the can end from the outlet end of the row. Can end conveying apparatus. 11. The apparatus of claim 10, further comprising: a magnet in which the magnetic means extends longitudinally along the row; And mounting means for supporting a magnet close to the row at a first longitudinal position along the row and distant from the row at a second longitudinal position along the row. An apparatus for heating a plurality of electrically conductive can ends, each of the can ends being disc shaped and having a curl around its circumference, the can ends being fed in-stick; A transport path having a longitudinal direction in which the can end moves and having a longitudinal segment; An induction coil at least partially surrounding a longitudinal segment of the transport path; And moving means for moving the can end in an in stick state along a longitudinal segment of the aqueous path. A transport path through which the workpiece moves in a longitudinal direction, wherein the transport path has a longitudinal segment; A pancake-type coil at least partially surrounding the longitudinal segment of the transport path and comprising at least one pancake subcoil; And a source connected to allow a current to flow through the at least one pancake-type subcoil, the source for changing the electric current. CLAIMS What is claimed is: 1. A method of handling a plurality of can lids, comprising: supplying the can lid in-stick; Heating the can lid in an in stick state; And at the same time, magnetically inducing the can cover in an in-stick state. CLAIMS What is claimed is: 1. A method of handling a plurality of can lids, comprising: inductively heating a can lid in a face-to-face relationship with each other; And at the same time, separating the can lids from each other by generating the magnetic field effective to separate the can lids in order to share a magnetic field. 21. The can lid handling method of claim 20, wherein the induction heating step comprises disposing a can lid in an oscillating magnetic field oscillating at an intermediate frequency. 22. The method of claim 21, further comprising moving the can lid along a transport path during heating. CLAIMS 1. A method of drying an aqueous adhesive material applied to an end of an electrically conductive can, comprising the steps of: supplying a can end to which a waterborne adhesive material has already been applied to a dryer inlet; Transporting the can end through the dryer in a face-to-face relation along a nonconductive support structure; During the transport step, an alternating magnetic field is applied to the can end to induce current flow in the can end to thereby heat the can end and to heat the applied adhesive material to remove moisture from the adhesive material. Adhesive material drying method comprising the step of flowing a. 24. The method of claim 23, further comprising generating a magnetic field that is effective to separate the end of the can so as to possess a magnetic field during the transport. An apparatus for heating a synthetic material applied to a can end, comprising: a non-conductive support structure for supporting the can end while the can end is transported in a face-to-face relation along a support; An alternating current source; An electrical conductor connected to said alternating current source and sufficiently adjacent said support to generate an alternating magnetic field within said support; And to transport the can end along side to side along the support, to induce a current flow in the can end and to heat the can end by the induction, thereby heating the composite applied to the can end. And a conveying device for conveying the end of the can past the alternating magnetic field. 26. The heating apparatus according to claim 25, wherein the transportation device transports the can end along the support portion with the surface in contact with the surface.