GB2319534A

GB2319534A - Electric coils : winding wire : bonding

Info

Publication number: GB2319534A
Application number: GB9724513A
Authority: GB
Inventors: Werner Fidi
Original assignee: Harman International Industries Inc
Current assignee: Harman International Industries Inc
Priority date: 1996-11-20
Filing date: 1997-11-19
Publication date: 1998-05-27
Also published as: AT404206B; DE19749810A1; ATA202696A; DE19749810B4; GB9724513D0

Abstract

Lacquered wire, which may be of any cross-section and insulated, is wound into electric coils, and the lacquer is softened by heating precisely at the point of winding, using possibly a gas flame or a focused laser beam. Wire tensioning ensures optimum packing of the windings. The lacquer fills hollows in, and bonds, the wound coils, which may be used for microphones, headsets or loudspeakers.

Description

2319534 fWWHOD OF -WMJFA=ING C6= The present invention relates to a method

of manufacturing coils of a cementing or baking lacquer wire having any chosen cross-section, wherein a high packing density of the coils is desired. The wire may be insulated. Preferably, in accordance with this method, coils may be produced for electrodynamic transducers for microphones, headsets and loudspeakers.

Electrodynamic transducers are composed of a diaphragm to which a coil is attached which, in turn, is located in a magnetic field arranged transversely of the axial direction of movement of the coil.

When sound impinges upon the diaphragm, the diaphragm is moved together with the wire attached thereto in the magnetic field, so that a voltage is induced in the coil, wherein the voltage can be used for further signal processing.

On the other hand, if a signal-dependant current flows through the coil, a proportional movement of the diaphragm and, thus, a corresponding sound radiation occur.

The coil is constructed from a usually insulated copper or aluminum wire which is held together by a cement or bonding agent.

This cement or bonding agent is usually applied to the coil wire in the form of a so-called cementing or baking lacquer.

The structure of such a known wire with cementing lacquer and the configuration of the coil are illustrated in Figs. 1 - 4 and in Fig. 7 of the drawing.

As is apparent from Fig. 1, the insulation layer 2 is applied directly on the electrically conductive metal core 1 and the cementing lacquer layer 3 is on the insulation layer 2. Depending on the intended use, the diameter of the wire 1 may be 0.02.0 to 1.0 wm. The thickness of the insulation layer 2 is approximately 0.005 - 0.015 mm while the thickness of the cementing lacquer layer 3 is in the order of magnitude of 0.01 to 0.02 mm.

The cementing lacquer layer has the property that it is softened when heat is applied and that it solidifies when it cools.

Depending on the intended use, the coils reach very different operating temperatures. While no temperature increase occurs during the operation of transducers for microphones, a temperature increase of up to 500C must be expected in headset transducers. In loudspeakers, the coils can even reach peak temperatures of 2000C.

In order to ensure that the coils are dimensionally stable at such peak temperatures, the softening temperature of the cementing lacquer used must always be higher than the operating temperature to be expected.

Accordingly, when manufacturing coils for electrodynamic transducers, heating of the cementing lacquer layer to the softening temperature always is of central importance. Heating can be carried out in various ways.

In accordance with a known method, for example, hot air is used which heats the cementing lacquer layer during winding or coiling. However, because of the low thermal capacity of air, only coils having a small mass and cementing lacquer layers with low softening temperature can be processed in accordance with this method. Accordingly, the method is only suitable for the manufacture of coils which are not heated or only insignificantly heated during operation. Typically, this method is used for the manufacture of coils for microphone transducers.

In DE 27 43 439 it is proposed to supply the heat for hardening the cement through the winding mandrel. Because of the relatively great mass of the winding mandrel, this method is not capable of realizing short cycle periods.

DE 27 09 407 discloses a method which utilizes electric current for heating the coil after winding to such an extent that the cement liquifies and is hardened.

Particularly in the case of multiple-layer coils, this method has the disadvantage that the temperature distribution cannot be uniform over the cross-section of the coil: the inner coil portions are inevitably heated more strongly than the outer coil portions because they can discharge heat to the outside. As a result, the cement is easily partially overheated which may lead to premature aging, but also to a complete destruction of the coil.

DE 44 19 252 discloses a manufacturing method in which ultrasonic energy is used for softening an insulation layer of an amide-imide polymer material. According to this method, an ultrasonic sonotrode is arranged in the interior of the winding mandrel and a counter-electrode is placed from the outside around the coil winding.

This method has the disadvantage that a complicated apparatus is required because a sonotrode must be mounted in the interior of a winding mandrel.

Mechanical means are also used for maintaining a dimensionally stable coil even at high operating temperatures. DE 23 53 301 proposes a cylindrical coil carrier which has a recess at the inside thereof, wherein the moving coil is glued into the recess.

DE 44 19 250 proposes to construct the coil carrier in such a way that the lower end can be bent upwardly and glued to the carrier in such a way that the coil is completely surrounded.

For reasons of cost, it is desirable when constructing an electrodynamic transducer to use magnets which are as small as possible. Consequently, for utilizing the magnetic filed in an optimum manner, it is necessary to arrange the windings of the coil with a packing density which is as high as possible.

When a wire is used as illustrated in Fig. 1, the individual electric conductors are positioned spaced apart from each other by twice the thickness of the cementing lacquer layer and the insulation layer, as schematically illustrated in Fig. 2.

The optimum packing density for round wires is shown in Fig. 3. This packing density is obtained when the insulation layers of the individual windings contact each other and the wires of the individual layers are always located precisely on top of each other. This is important in order to achieve a uniform coil structure. This is because if the windings end up being located in the depressions of the previous layer, the wire must always be guided at the beginning of each new layer during a revolution in an uncontrolled manner over the last winding of the previous layer, which inevitably results in irregularities of the coil structure. However, a uniform coil structure is necessary because the thickness of the coil must fit precisely into the air gap.

Another possibility for achieving a high packing density is to use a wire having a rectangular cross-section, as already mentioned, for example, in DE 24 34 796. However, this possibility which at first glance appears to be an elegant solution, has several significant disadvantages.

When wires are drawn already with a rectangular crosssection, special measures must be taken during the subsequent coating to ensure that the insulation layer and the cementing lacquer layer have the necessary thicknesses even at the edges. Consequently, the costs of these wires are disproportionately high.

It is also possible to squeeze insulated round wires prior to winding in such a way that they have an essentially rectangular cross-section. Fig. 7 is a partial illustration of a coil cross-section made of wires of this type. Carrying out this squeezing procedure is technologically difficult because it always must be ensured that the insulation layer is not damaged by the deformation.

The winding of rectangular or essentially rectangular wires is complicated because the wires must always be guided with the correct positioning during winding.

Even when using wires having rectangular or essentially rectangular crosssections, it is not possible to achieve the maximum possible packing density because the wire crosssection is surrounded by the insulation layer and the cementing lacquer layer. For the case of equally thick cementing lacquer layers 3 as shown in Fig. 1, Fig. 4 schematically shows the conditions for rectangular wire and Fig. 7 shows the conditions for essentially rectangular wire. As can be clearly seen, it is not possible to achieve the optimum packing density as is the case in Fig. 3.

For manufacturing coils for electrodynamic transducers, the use of wires having circular cross-sections is desirable because they are inexpensive and can be wound easily. optimum results can be achieved if the individual windings can be arranged in such a way that their insulation layers do contact each other.

Therefore, it is the primary object of the present invention to provide a method of manufacturing coils of the type discussed above in which the disadvantages of the prior art methods are eliminated.

In accordance with the present invention, a coil for electrodynamic transducers for microphones, headsets and loudspeakers is manufactured by supplying heat essentially precisely concentrated at the winding location, so that the cementing lacquer layer is liquified and the wires are placed by the necessary pretension during winding in such a way that an optimum packing density is achieved. The cement is pressed into the hollow spaces of the coil as a result.

The method according to the present invention also makes i possible to wind bare wires into coils if the precisely concentrated heat discharge liquifies only the outermost cementing lacquer layer. This constitutes an advantage with respect to manufacturing technology and costs.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.

In the drawing Fig. 1 is a cross-sectional view of an insulated wire with cementing lacquer layer; Fig. 2 is a cross-sectional view of two insulated wires with cementing lacquer layers positioned next to each other; Fig. 3 is a sectional view of a detail of a coil in which the insulated round wires including cementing lacquer layer are arranged with an optimum packing density; Fig. 4 is sectional view of a detail of a coil of insulated wires with cementing lacquer layer, wherein the wires have a rectangular cross- section; Fig. 5 is a perspective view of a winding mandrel; Fig. 6 is a perspective view showing the winding mandrel with a gas flame; and Fig. 7 is a sectional view of a detail of a coil of insulated wires with cementing lacquer layer, wherein the wires have an essentially rectangular cross-section.

Winding of a coil is usually carried out on a rotating winding mandrel, wherein the winding tension of the supplied wire is maintained constant by a wire uncoiler. An adjustable feed ensures the correct positioning of the wire.

Fig. 5 shows the most important components of the winding procedure and of the winding apparatus. A coil wire 4 is fastened in a groove 7 of a flange 5 of a winding mandrel 6. By rotating the winding mandrel in the direction of arrow 14, the wire 4 is wound into a coil. A guiding device 8 ensures feeding of the wire 4. The feeding device 8 is moved forward and backward in the direction of double arrow 13 by the spindle of the winding mandrel 6 through a gear unit.

In accordance with the invention, the cementing lacquer layer is liquified during winding by applying heat at the winding location 9 over a heating zone having approximately twice the size of the wire cross- section until the supplied wire is placed by the winding tension next to the wire of the preceding winding in such a way that the insulation layers of both wires contact each other. Consequently, the liquified cement is forced into the hollow spaces of the coil, as already illustrated in Fig. 3.

Due to the rotation of the winding mandrel 6, the cement is heated only temporarily and can solidify again immediately after leaving the winding location 9.

In accordance with a preferred development of the present invention, a gas flame is used for the accurately concentrated and quick heating of the wire during winding. An embodiment of the invention is schematically illustrated in Fig. 6. A nozzle 10 is mounted on an arm 11 which swings the nozzle 10 into the intended position after the start of the winding process. In this manner, during the time that no winding is carried out, the flame 12 can be moved into a position in which the operator is not in danger and the winding mandrel cannot be damaged.

The diameter of the heating zone can be adjusted by the selection of a suitable nozzle diameter. In accordance with the invention, the gas flame should always be positioned in such a way that the heating zone in which the cement is liquified is located precisely at the winding location 9. For this purpose, it is necessary to move the gas flame back and forth parallel to the double arrow 13 by means of a feeding mechanism during winding precisely in the manner the wire is moved.

- is - The gas flame must have such a high temperature that, in the short time during which the wire is moved through the heating zone, such a quantity of heat is transferred to the cement that the cement is essentially liquified. Immediately after leaving the heating zone, the cement is solidified and the coil wires are secured in their position as a result.

Accordingly, the coil wires are glued together directly during winding, so that a quick and inexpensive manufacture of coil is possible.

In actual practice an oxyhydrogen gas flame, as it known from soldering technology, has been used successfully. This flame develops a temperature of about 3,OOOOC and can be easily adapted to the size conditions of a coil winding device by using nozzles having diameters of as little as 0.2 mm.

The present invention is not limited to the use of a gas flame. Suitable for carrying out the present invention is any essentially exactly concentrated supply of heat that has such a magnitude that the cement layer can be temporarily liquified. For example, it is also possible to use a focused laser beam for transferring the necessary heat quantity.

Particularly suitable for this purpose appear to be highpower diode lasers because they are particularly suitable to be mounted in existing winding machines because of the fact that they are of compact construction and can be easily controlled.

The use of a plasma method or an electron-beam device appear also possible if they can be set up in such a way that high temperatures can be produced at the winding location.

The method of manufacturing coils according to the present invention basically can also be used with cements which harden as a result of a chemical reaction when heat is applied, for example, as is the case in socalled two-component adhesives. However, in this case, it is necessary that the reaction time of the adhesive is so short that hardening takes places during the short period of time in which the adhesives traverse the heating zone.

The method according to the present invention for manufacturing coils of an electrodynamic transducer is suitable for wires of any cross-section. Preferably, as already mentioned, wires having round cross-sections are used. In that case, the windings will be placed in such a way that the insulation layers of adjacent windings contact each other along a line. The cement is displaced form the contact locations to the hollow spaces between the coil wires. As a result, an optimum packing density, a secure adhesion and a short manufacturing time are achieved.

However, it is also possible to process wires having any chosen crosssectional shape in accordance with the method of the present invention. For example, Fig. 7 shows the conditions when an essentially rectangular wire cross-section is used for a cementing lacquer layer having the same thickness as in Fig. 1. It is clearly apparent that also in this case the cement or adhesive 3 is displaced into the hollow spaces between the coil wires and ensures that the windings are securely held together.

All coils which are produced in accordance with the method of the present invention have a higher packing density than those coils that are produced in accordance with a previously known manufacturing method.

Moreover, because gluing occurs during winding, the cycle period when manufacturing coils is drastically reduced, so that the manufacturing method according to the present invention is extremely efficient and inexpensive.

This is particularly the case when manufacturing coils having high copper volumes because, in accordance with the state of the art, these coils had to be hardened after winding by means of an electric current or by heating in a heating cabinet.

Another advantage of the manufacturing method according to the present invention is the fact that commercially available winding machines can be easily adapted to the new method. The nozzle for a gas flame is connected easily and only through a thin hose to the gas generator. Fastening the nozzle on a feeding mechanism should not generally pose any difficulties because only external manipulations must be carried out on the machine.

The swinging movement of the nozzle into a position which is safe for the operator can be controlled through the operation sequence program and can be carried out electrically or pneumatically.

The same is analogously true when using a diode laser. Also in this case, only the optical system and the laser itself has to be fastened movably at the machine, while the current supply and the control can be mounted separately.

While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

Claims

CLAIMS:

1. A method of manufacturing coils provided externally with a cementing lacquer layer, the method comprising softening the cementing lacquer layer during winding of the coil by supplying heat, and carrying out the heat supply during winding of the coil essentially in a precisely concentrated manner and liquefying the cementing lacquer layer at a winding location.

2. insulated.

The method according to claim 1, wherein the wire is

3. The method according to claim 1, comprising supplying heat through a gas flame.

4. The method according to claim 3, wherein the gas flame is an oxyhydrogen gas flame.

5. The method according to claim 1, wherein the heat supply is effected through a focused laser beam.

6. The method according to claim 1, wherein, for obtaining an optimum packing density, liquified cementing lacquer is displaced into intermediate spaces between the wire by tension acting on the wire during winding.

7. A method of manufacturing coils substantially as hereinbefore described with reference to and as shown in the acconipanying drawings.