ELECTROMECHANICAL MACHINE ARMATURE HAVING A PROTECTIVE COATING

FIELD OF THE INVENTION The present invention relates to protecting the winding heads of an electromechanical machine armature from an airflow which, especially in the case of power tool motors, can contain abrasive material such as metal dust, concrete dust, sand, or dirt that is moving at high speeds. Such airborne abrasive material can damage the wires and/or its insulation by impact, erosion, etc. Of course electromechanical machines used for other applications may also benefit from such protection.

BACKGROUD OF THE INVENTION

Prior art methods for protecting the winding heads of such machines include adding protective coverings, such as baskets, ropes, or lines of jelly glue or viscous resin to protect the turning armature. AU of these methods add some kind of geometrically defined parts to the winding head. These parts can be expensive or require expensive manufacturing processes. Other methods such as injection molding are also possible. Each of these methods can also raise issues concerning balancing as well as electrical and thermal insulation. JP Patent Appl. No. 07-039098 describes impregnating a resin-sealed electric motor armature with magnetic and non-magnetic particles, but not for the purpose of protecting the winding head. It would be useful to have a low-cost solution that still adequately protects the winding head from damage.

SUMMARY OF THE INVENTION An electromechanical machine is described comprising an armature, at least one insulated wire wound around the armature to form an insulated wire winding with an external surface, and binding means in contact with at least a portion of the external surface and which is impregnated with a plurality of electrically non-conductive coating particles. The coating particles have the advantage that they form a barrier that protects the winding heads in particular from damage from abrasive material that may be

directed at the armature winding heads at high speeds. In other words, they serve to form a layer of protection for the insulated wire winding.

One possible coating is "fur-like" in that the majority of the coating particles are partially submerged in the binding means. This simplifies manufacture in that the coating particles can be applied after the binding means, for example a resin, is applied to the armature windings. Some particles are partially submerged and retained as a coating when the resin hardens.

A second possible coating is "crust-like" in that the majority of the coating particles are entirely submerged in the binding means. This has the advantage that the coating particles will be better retained by the binding means and less likely to detach when the armature is spinning at high speeds or is struck by an impact from an airborne particle.

Various varieties of coating particles are possible and such particles may be quite inexpensive and readily available if they are selected from the group consisting of plastic, sand, glass, or ceramic materials.

To best protect the winding ends from impacts, it is advantageous if the protective coating is formed in at least one layer which substantially covers its external surface. To provide further protection, more than one layer, at least one of which substantially covers the external surface may be provided. The additional layer or layers provide a backup if some particles detach from the armature or are damaged over time.

A uniform and reliably repeatable coating is most easily achieved if the coating particles are substantially uniform in size, shape, and composition. However, there may be advantages to applying coating particles that are substantially non-uniform in either size, shape, composition, or in any combination of these factors. For example, a less abrasive coating can be applied directly to the winding with a more abrasive external layer. Large and small particles might be advantageously mixed to provide more complete coverage

in under certain application manufacturing conditions.

The protection for the armature as described herein can be used for any sort of electromechanical machine armature, but it is best suited for the small electric motors that are used in power tools, and especially cutting, sawing or drilling tools that generate small abrasive particles during operation.

A preferred and inexpensive method for manufacturing an electromechanical machine with the protective coating is disclosed, wherein at least one insulated wire is wound around an armature to form an insulated wire winding with an external surface, binding means of uniform composition is applied to the external surface and a plurality of coating particles are applied to impregnate the binding means. This method has the advantage that it can be coordinated with the state of the art resin trickling process that is used for sealing the windings, involving only the additional step of applying the coating particles. In addition, if the trickling process is accomplished in several steps, the coating particles can be additionally coated or applied in several layers to form a more durable protective coating.

In order to better direct the coating particles to the external surface of the winding, means for providing positive air pressure can be advantageously used. Once the coating particles are submerged in the binding means, they can be compressed by other means, such as solid, liquid or gas pressure in order to make the protective coating more uniform and compact. This can enhance its ability to protect the end windings.

BRIF DESCRIPTION OF DRAWINGS

Figure 1 is a schematic drawing of a first embodiment for an armature and apparatus for coating an armature with impact- and/or abrasion-resistant particles. Figure 2 is a schematic drawing of a second embodiment for an armature and an apparatus for coating an armature with impact- and/or abrasion-resistant particles. Figure 3A is a schematic drawing of a partial cross section of a coated wire winding

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with a single layer of coating particles forming a fur-like coating. Figure 3B is a schematic drawing of a partial cross section of a coated wire winding with a single layer of coating particles forming a crust-like coating. Figure 3C is a schematic drawing of a partial cross section of a coated wire winding with multiple layers of coating particles of uniform type.

Figure 3D is a schematic drawing of a partial cross section of a coated wire winding with multiple layers of coating particles of non-uniform type.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of a conventional electric motor armature 10 is illustrated in Fig. 1. The armature is provided with a lamination stack 12 defining longitudinal slots 14 into which one or more insulated copper wires 16 are wound to form coils or windings 17 with an external surface 18 around individual laminae. Ends of the copper wires 16 make electrical contacts to a commutator 19 at one end of the armature 10 providing means for feeding current to the wires 16 to form an electromagnet, hi conventional use, such an armature 10 rotates within a stator (not shown) to provide useful work by way of its armature shaft 20. A motor is described by way of example, but the invention is applicable to any electromechanical machine with wire windings, including motors and generators.

hi order to limit vibration, stretching, and noise from circulating air in the windings 17, as well as to a protect from impregnation by moisture and dust, the winding ends 22, 24 of the armature 10 are treated with relatively low viscosity liquid-phase resin 26 via a well-known trickling process. The armature 10 is rotated slowly, and resin 26 is applied via gravity to the rotating armature 10 where it is drawn into the windings of the insulated copper wire 16 via capillary action. Normally the resin 26 is applied contemporaneously to both winding ends 22, 24 so as to saturate the entire winding before it solidifies.

When such a thin resin 26 is applied as described above, there is little additional

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protection for the winding ends 22, 24. The wires 16 themselves typically have insulation that is about 0.05mm thick. The additional coating provided by the resin 26 may be much thinner in comparison, being normally less than 0.05mm and perhaps only 0.02mm thick. Even when solidified, the resin 26 is not very resistant to abrasive elements that may impact the winding ends 22, 24 at high speeds.

The present invention makes use of this prior art resin trickling process to provide a basis for introducing a protective coating to the armature 10. During or after the trickling process, a coating is applied which is made up of numerous individual coating particles 28, each themselves very small. Depending on how and when they are applied, the coating can be either fur-like (see Fig. 3A) or crust-like (see Fig. 3B). A range of materials, either organic or non-organic, can make for suitable coating particles 28, for example plastic, sand, glass fiber, ceramic material, or a mixture of some of these materials. The particles 28 can also be composed of metal, although it is preferred that a generally electrically non-conductive material is used to improve electrical insulation of the end winding. Furthermore, in comparison with other materials, the sharpness of individual metal particles might more frequently transduce external impacts to internal abrasion via transfer of momentum. However steel particles would have the advantage that their thermal conductivity would help promote heat transfer between the wires 16, lamination stack 12 and external air so that the motor runs cooler.

The coating particles 28 may range in size and shape. They can be little chips, grains, fibers, flakes, a mixture of some of these shapes, or perhaps a mixture including different sizes of a similar shape or different shapes and sizes altogether. A preferred shape and size for the coating particles 28 is a flake with dimensions of approximately 1.0mm X 1.0mm X 0.05mm although smaller or larger dimensions are possible. If fibers are used, they are preferably 1.0-2.0mm in length and 0.05mm in diameter. If the coating particles 28 are generally spherical in shape, then they preferably would have smaller diameters in the case of a fur-like coating so that they are sufficiently embedded in the thin layer of resin to be secured. However if they are submerged in the resin to

form a crust-like coating, then larger diameter spherical-shaped particles are possible.

During the manufacturing process, means are provided for applying particles 28 to the armature, for example by gravity feed through a funnel 30 (see Fig. 1). In a simplest case, at the conclusion of the trickling process, the armature could be rotated under such a funnel 30, so that coating particles 28 become partially submerged in the resin 26, resulting in a fur-like coating in the case of certain materials. Once the resin 26 hardens, the protective coating is fixed in place.

Alternatively the coating might be applied in several steps, or preferably applied in steps during or in-between steps of the trickling process. For example, the manufacturing process may consist of several stations on an assembly line. Instead of a one-time trickling process, the application of the resin 26 might be broken up into 2 or more, and preferably 7 or 8, partial trickling steps, each lasting for example less than a minute.

In such a situation, the particles can be applied in-between two trickling steps. The trickling step that follows application of the particles 28 would provide a coating for the particles 28 as well, so that they are fully submerged in the resin 26 forming a single layer.

If there are 3 or more steps in the tricking process, the particles can be applied 2 or more times in-between these steps. As such, there could be multiple layers of particles 28, each with resin in-between (see Fig. 3C). Such steps can follow immediately, before the resin 26 has solidified, or there could be one or more solidification steps in-between.

If there are multiple layers, they may be of similar or different particles 28. For example, less abrasive internal particles 29 might be applied first to the winding ends 22, 24 followed by a more abrasive particles 31 (see Fig. 3D). Depending on design considerations, it is up to the manufacturer to determine whether the particles 28 in each

layer would be densely or sparsely distributed, or whether they should be uniformly or not so uniformly distributed. If the particle applying means is a simple funnel 30 which uses gravity to apply the particles 28, then it should be provided with means for opening and closing the funnel such as a door 32, so as to limit waste or mess in the coating process.

To protect the lamination stack 12 from receiving coating particles 28 where they are not needed or desired, a mask 34 could be used in the manufacturing process to block off regions of the armature 10 that should be kept clean.

More sophisticated and directed means could also be used for directing the coating particles 28. to the winding ends 22, 24. For example means for providing positive pressure via pulses of air, such as a tank of compressed air 36 (illustrated schematically in Fig. 2), can be used to more specifically direct the particles to a particular location, which would lead perhaps to more consistent and reliable results. Such air pressure might also help to better distribute the coating or decrease clumping of particles 28, etc.

To further improve the efficiency with which the particles adhere to the armature 12, either the coating particles 28 or the armature 10 can be loaded with electrostatic charge before the coating is applied. This should increase the stickiness of the particles 28 to the spinning armature 12, thereby decreasing waste.

It is also contemplated that other carrier media besides liquid resin 26 can be used for securing the coating particles. For example, once the resin 26 has solidified, the armature 10 could receive a layer of glue or other carrier, onto which the coating particles 28 can be applied. Alternative coatings, such as powdered resins could be used in both the early and late steps of the coating process. When heated, such powders liquefy, and as such can be used to retain the coating particles 28.

There may be advantage to providing means such as a blunt solid object 38 to pat-down

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or press the particles together to form a more compact and uniform coating. For example in the textile industry, there is a process by which colored flakes are applied to a garment and then compressed in order to give the appearance of a homogenous layer without air gaps. Alternatively hydraulic pressure from a liquid or alternatively gas delivered at high pressure could be used to accomplish the same purpose.

Another alternative is to introduce the coating particles 28 directly into the resin 26 before the resin is used in the trickling process. As described already, the particles 28 should be sufficiently small that they permit the resin 26 to flow into the winding ends 22, 24 via capillary action, while at the same time provide some measure of protective coating. It may be difficult however to create a coating that covers the entire surface of the winding ends 22, 24 with this method, not to mention the fact that there may need to be modifications to the trickling process apparatus to make sure there is no clogging, etc. by the coating particles.

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