Photoetched Induction Coil Assembly

Abstract

An induction coil assembly includes circuits photoetched on metallic laminates bonded to a flexible substrate. The substrate is wound on an arbor and pinned, after which it is removed from the arbor, impregnated and machined to provide an induction coil having close mechanical and electrical tolerances.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to induction coils of the type used in gyro torquer assemblies and, more particularly, to induction coils of the type described having photoetched circuitry.

2. Description of the Prior Art

Prior to the present invention, induction coils were hand wound. The coil so provided was then encapsulated and machined as required. It is difficult and costly to control mechanical and electrical tolerances within limits required for modern applications when providing induction coils in this manner.

SUMMARY OF THE INVENTION

The present invention contemplates an induction coil assembly having circuitry in the form of a geometric pattern of conductive metal photoetched in a planar arrangement on a flexible substrate. The flexible substrate is wound on an arbor, with locating tabs being provided on the substrate to insure predetermined spacing between windings. A registration pin is inserted through the tabs to prevent the substrate from unwinding, after which the wound substrate is removed from the arbor, vacuum impregnated to fill the voids between and around the windings and machined as required.

One object of this invention is to provide an induction coil having photoetched circuitry.

Another object of this invention is to provide an induction coil of the type described whereby electrical characteristics can be predetermined with a high degree of repeatability.

Another object of this invention is to provide a method for manufacturing an induction coil of the type described which permits greater control of manufacturing tolerances than has heretofore been possible.

Another object of this invention is to manufacture an induction coil of the type described at a lower cost than has heretofore been possible.

The foregoing and other objects and advantages of the invention will appear more fully hereinafter from a consideration of the detailed description which follows, taken together with the accompanying drawings wherein one embodiment of the invention is illustrated by way of example.

It is to be expressly understood however, that the drawings are for illustration purposes only and are not to be construed as defining the limits of the invention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially sectioned side view of a flexible substrate according to the invention and having metallic laminations on either side thereof.

FIG. 2 is a partially sectioned side view showing the flexible laminated substrate of FIG. 1 with plated through holes for electrically connecting the metallic laminations.

FIG. 3 is a side view showing the flexible laminated substrate of FIGS. 1 and 2 having circuit patterns etched on the metallic laminations.

FIG. 4 is a diagrammatic representation showing the geometric form of the etched circuit patterns, with said patterns being connected by the plated through holes.

FIG. 5 is a top view of the etched flexible laminated substrate.

FIGS. 6, 7 and 8 are pictorial representations showing the laminated substrate of FIGS. 1-5 wound on an arbor and machined to provide a final induction coil in accordance with the invention.

DESCRIPTION OF THE INVENTION

FIG. 1 shows a flexible, continuous substrate 4 having metallic laminations 6 and 8 on either side thereof. Substrate 4 may be a suitable polyimide plastic such as that carrying the trade name Kapton and marketed by Du Pont Company, and is approximately 0.002 inches thick. Laminations 6 and 8 may be one ounce copper strips (0.0014 inches thick) suitably bonded to substrate 4 as is well known in the art.

Holes 10 are drilled through substrate 4 and metallic laminations 6 and 8 at predetermined locations along the length thereof as shown in FIG. 2. The holes are then conventionally plated through with a suitable conductive material such as copper, with plated through holes 10 thereby providing electrical connections between metallic laminations 6 and 8.

Laminations 6 and 8 are etched by conventional photochemical methods to provide circuit patterns designated by the numerals 14 and 15, respectively, as shown in FIG. 3. Plated through holes 10 connect circuit patterns 14 and 15 as shown in the figure.

Thus, as seen in FIG. 4, circuit pattern 14 includes a single planar coil 16 and a pair of connected planar coils 17 and 18, with the pattern, i.e. a single coil and a pair of connected coils, being repeated along the length of substrate 4. Circuit pattern 15 includes a repeatable pattern of a pair of connected coils 19 and 20 and a single coil 21. Single coil 16 in circuit 14 is connected by a plated through hole 10 to coil 19 in circuit 15. Another plated through hole 10 connects coils 17 and 20 while still another plated through hole 10 connects coils 18 and 21. It will now be understood that in this manner a continuous electrical circuit is provided along the length of substrate 4.

The completed photoetched substrate has a configuration as shown in FIG. 5, wherein only circuit 14 is shown. Substrate 4 further includes locating tabs 22 which are positioned to allow a space of approximately 0.002 inches between windings when the substrate is wound on an arbor and the tabs aligned as will be hereinafter explained. Tabs 22 have holes 24 therethrough to accommodate a registration pin 28 shown in FIG. 7.

As shown in FIG. 6, photoetched substrate 4 is wound on an arbor 25. Locating tabs 22 are positioned to allow the aforenoted 0.002 inch space between windings when the substrate is wound on the arbor and the tabs aligned as shown in FIG. 7, with the space between windings carrying the description A. Registration pin 28 is inserted through holes 24 in tabs 22 to prevent the substrate from unwinding as will now be understood.

After substrate 4 has been wound and pinned, the assembly is removed from arbor 25 and vacuum impregnated so as to fill the voids between and around the layers with a suitable insulating material 30 such as an epoxy resin as shown in FIG. 8. After vacuum impregnation has been completed, locating tabs 20 and pin 28 are sheared off and the inner and outer diameters of the assembly are machined as required to provide a finished coil assembly as showin in FIG. 8.

It will now be seen that an induction coil having the configuration shown in the drawings and manufactured by the method described has certain advantages. First, since circuits 14 and 15 are photographically produced, each and every coil 16-21 (FIG. 4) will be precisely the same. Thus, inductor widths and conductor spacing can be controlled to the extent that electrical characteristics such as impedance and capacitance can be predetermined with excellent repeatability. Also the photoetching process lends itself to greater control of manufacturing tolerances. Due to the good repeatability and dimensional control, gaps can be reduced with a subsequent increase in torque being thus provided when a torquer application is intended. Finally, a coil assembly manufactured according to the invention can be achieved at a cost greatly reduced from that required for coil assemblies manufactured as now known in the art.

Although but a single embodiment of the invention has been illustrated and described in detail, it is to be expressly understood that the invention is not limited thereto. Various changes may also be made in the design and arrangement of the parts without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art.

Claims

What is claimed is:

1. A coil assembly, comprising:

a flexible, continuous substrate;

conductive circuit patterns on both sides of the substrate;

means connecting the circuit patterns on one side of the substrate with those on the other side and providing a continuous circuit along the length of the substrate;

locating tabs at predetermined points along the length of the substrate;

said substrate with the continuous circuit thereon wound with the locating tabs in alignment to provide predetermined spaces between windings; and

an insulating material in and around said spaces.

2. A coil assembly as described by claim 1, wherein:

the conductive circuit patterns are geometric patterns of conductive metal in a planar arrangement on both sides of the substrate.

3. A coil assembly as described by claim 1, wherein:

the means connecting the circuit patterns on one side of the substrate with those on the other side and providing a continuous circuit along the length of the substrate includes through holes plated with a conductive metal.

4. A coil assembly as described by claim 1, wherein the conductive circuit patterns on both sides of the substrate include:

a repeatable pattern of a single planar coil and a pair of connected planar coils on one side of the substrate; and

a repeatable pattern of a pair of connected planar coils and a single planar coil on the other side of the substrate.

5. a coil assembly as described by claim 4, wherein the means connecting the circuit patterns on one side of the substrate with those on the other side and providing a continuous circuit along the length of the substrate includes:

a through hole plated with a conductive metal connecting the single planar coil on the one side of the substrate to one of the connected pair of planar coils on the other side;

another plated through hole connecting one of the connected pair of planar coils on the one side of the substrate with the other of the pair of coils on the other side; and

still another plated through hole connecting the other of the pair of coils on the one side of the substrate with the single planar coil on the other side.