Electromagnetic coil assembly employing spool-spindle

An electromagnetic coil assembly comprising a spool-spindle and a case. The spool-spindle comprises a spindle portion and a larger included portion. The spindle portion has a conductor wound thereon. The larger included portion has opening for receiving the conductor. The case has a first case end and a second case end, with an opening extending through the case. A first internal surrounding surface extends from the second case end and a second surrounding internal surface having a smaller diameter extends from the first case end. The first internal surrounding surface meets the second internal surrounding surface at an annular internal wall. The spool-spindle is positioned in the case until the larger include portion abuts against the annular internal wall, and the case and spool-spindle are joined.

FIELD OF THE INVENTION

The present invention relates to an electromagnetic coil assembly comprising a spool-spindle with wound conductor used for generating an electromagnetic field.

BACKGROUND

An electromagnetic coil assembly typically includes a case. Internal to the case is a spindle with a conductor or wire wound around the spindle. The conductor is typically helically wound around the spindle. One example of use of electromagnetic coil assemblies such as these is in combination with drug pumps and drug delivery control valves.FIG. 1shows a sectional view of a prior art electromagnetic coil assembly used in such devices, and reference may be made to U.S. Pat. No. 6,264,439 for a more detailed description thereof.

Briefly, the prior art electromagnetic coil assembly shown inFIG. 1has a case20, and internal to the case is a spindle12. The case20is typically a manufactured part made by a turning process, and the case defines an opening that is symmetric about an axis of revolution. The spindle12is also typically a turned part that is symmetric about its principal axis and is of ferromagnetic material. The wire coil or conductor winding14is helically wound around a central portion of the spindle, and when current passes through the coil an electromagnetic field is generated. The prior art electromagnetic coil assembly also includes a washer16pressed onto one end of the spindle and a locater or spacer18pressed onto the other end of the spindle. The washer and locater are press fit onto opposite ends of the spindle and held thereon by a friction fit. Fixturing is employed to hold all the components in place while the case is being filled with a potting compound or epoxy24, and while the epoxy cures. The epoxy is added in two separate phases or steps. The case is then fitted to an electromagnetic device26.

In the prior art, the combination of the washer and the locator serve to center the spindle within the case. The washer, however, does not fully constrain the spindle, and the spindle can therefore travel, along with the associated washer, in the direction of its principal axis. When the coil case is filled with potting epoxy, the spindle is locked in position. Furthermore, if there is no locator, the free end of the spindle opposite the washer additionally must be held concentric with the case and constrained in the axial direction until the potting compound has cured. Fixturing establishes the distance from the washer end of the spindle to the plane established by the washer end of the case.

What is needed is an improved electromagnetic coil assembly and method that does not require washers, provides for improved stability of components, decreases production time, and reduces fixturing requirements.

SUMMARY

The electromagnetic coil assembly of the present invention comprises a spool-spindle that is joined to a case. The spool-spindle comprises a spindle portion and a larger included portion that is joined to or integral with the spindle portion. The spindle portion and larger included portion is of ferromagnetic or conductive material and has a coil wound thereon. The larger included portion also defines an opening through which a conductor(s) of the coil can extend and through which epoxy can be introduced.

More specifically, the spool-spindle comprises a first end and an opposed second end, and the larger included portion is positioned between the first end and the second end. Also, the larger included portion comprises a first spool surface, an opposed second spool surface, and a surrounding spool surface that extends between the first spool surface and the second spool surface. A chamfer can be formed in the larger included portion between the surrounding spool surface and the second spool surface.

The case to which the spool-spindle is joined comprises a first case end and a second case end, with a cylindrical shaped outer surface extending between the first case end and second case end. An open region is defined in the case extending from the first case end to the second case end. The case further comprises a first internal surrounding surface extending from the second case end in a direction toward the first case end, and a second internal surrounding surface extending from the first case end in a direction toward the second case end. The first internal surrounding surface has a greater diameter than the second internal surrounding surface, and the first internal surrounding surface and the second internal surrounding surface meet at an annular internal wall. The annular internal wall provides a shoulder or stop for the larger included portion of the spool-spindle to abut against when it is positioned in the case.

The electromagnetic coil assembly is made by providing the above-described case and spool-spindle, winding a conductor around the spindle portion of the spool-spindle, moving the spool-spindle into the case until the larger included portion abuts against the annular internal wall, and joining the spool-spindle and the case together. The joining can be by friction fit, welding, crimping, and the like. Electrical potting epoxy is introduced into the assembly to fill the spaces between the spool-spindle, coil, and case.

Some of the advantages of an electromagnetic coil assembly employing the spool-spindle are that fewer components need to be manufactured, assembly steps are eliminated, and dimensional accuracy of the final assembly is easier to control because there are fewer component interface locations.

DETAILED DESCRIPTION

FIG. 2is a sectional view of the electromagnetic coil assembly30of the invention. The electromagnetic coil assembly30comprises a case32and a spool-spindle34. As shown, the spool-spindle34is centrally positioned inside the case32. The electromagnetic coil assembly30further comprises a conductor winding31that is wound around the spool-spindle34to form a coil for generating an electromagnetic field.

As shown inFIGS. 2-4,6-8, the spool-spindle34has a first axial end42and an opposed second axial end44. The spool-spindle34includes a spindle portion36that extends from the first end42to a larger included portion45, and the spindle portion36and larger included portion45are joined to one another. In one of the preferred embodiments, the larger included portion45is formed integral with the spindle portion36, as shown inFIGS. 7 and 8, for example being machine turned from a single piece of material.FIG. 8is a sectional view of the spool-spindle34taken along cut line C-C ofFIG. 7. The larger included portion45has a larger diameter designated D1inFIG. 8, and the spindle portion36has a smaller spindle diameter designated D2inFIG. 8, as compared to the larger diameter designated D1. As shown, the spindle portion36in is in the form of a rod or shaft, and the larger included portion45is in the form of a disc.

The spool-spindle34further comprises an extension portion37, as shown inFIGS. 2-4, and6-8. The extension portion37extends axially from the second end44of the spool-spindle34to the larger included portion45, and is joined to the larger included portion45. In one of the preferred embodiments the extension portion37is formed integral with the larger included portion45. Also, the diameter of the extension portion37can be the same as the diameter D2of the spindle portion36.

As shown inFIGS. 7 and 8, the larger included portion45defines a first spool surface47and an opposed second spool surface49. In one of the preferred embodiments, a lead-in chamfer48is formed in the larger included portion45. The lead-in chamfer48is used for facilitating the assembly of the spool-spindle34in case32. A surrounding or peripheral spool surface39extends around the larger included portion45. In particular, and as shown inFIG. 8, the surrounding spool surface39extends between the lead-in chamfer48and the first spool surface47. The first spool surface47extends from the surrounding spool surface39to the extension portion37, and the second spool surface49extends from the lead-in chamfer48to the spindle portion36. It is noted that in other embodiments, the lead-in chamfer48can be eliminated.

Also, the larger included portion45defines spool openings46used for receiving a conductor(s)31and/or used for allowing potting compound or epoxy38to be introduced into the case32. As shown inFIG. 6, the longitudinal axis of the spool-spindle34is designated A.

The above-described spool-spindle34is sized to be positioned inside the case32. The case32is a hollow cylindrical-shaped body40as shown inFIG. 4. As shown inFIG. 5, the case32has an outer surface50, a first case end54, an opposed second case end56, and defines an open region58, as shown inFIGS. 4 and 5. Additionally, at the first case end54the case32has an annular formation55that extends into the case open region58. The case32has a longitudinal axis designed B inFIG. 5that extends through the open region58.

Additionally, the case32has a first internal surrounding surface60having a first diameter extending from the second case end56. The first internal surrounding surface60extends toward the first case end54, until it meets an annular internal wall62. At the annular internal wall62the first internal surrounding surface60meets a second internal surrounding surface64. The second internal surround surface64has a diameter less than the diameter of the first internal surrounding surface60. The annular internal wall62defines a shoulder which serves as a stop for the spool-spindle34, as will be described presently.

To assemble the electromagnetic coil assembly30, the conductor31is wound around the spindle portion36of the spool-spindle34. Then, the case32and spool-spindle34are axially aligned, such that the longitudinal axis designated A of the spool-spindle34and the longitudinal axis designated B of the case32are coincident. This arrangement is shown inFIG. 4. Then, the first end42of the spool-spindle34is moved through the open region58. It is noted that in order for the spool-spindle34to be moved into the case32, the diameters of the spindle portion36and the larger included portion45are less than the diameter of the first internal surrounding surface60of case32.

As the spool-spindle34continues to be moved longitudinally into the case32, the lead-in chamfer48formed in the larger included portion45contacts the annular internal wall62. As movement continues, the larger included portion45seats against the annular internal wall or shoulder62. Movement of the spool-spindle34into the case32stops, because the diameter D1of the larger included portion45is greater than the diameter of the second internal surrounding surface64. Thus, the internal wall62acts as a stop, and controls the distance the spool-spindle34can be inserted into the case32.

By virtue of the relative dimensions of portion45and the first internal surrounding surface60, the spool-spindle34and case32are joined to one another by a press fit or an interference fit. In other embodiments, the spool-spindle34and case32may be joined by welding, pinning, crimping, and mechanical fasteners. In another embodiment, the first internal surrounding surface60of the case32may be provided with an internal thread, and the surrounding spool surface39provided with an external thread, so that the case32and spool-spindle34can be threaded together. This threading may be reversed, such that the first internal surrounding surface60has an external thread, and the surrounding spool surface39has an internal thread.

After assembly, a first plane passes through the first case end54surface, such that the first plane is substantially perpendicular to the longitudinal axis of the case32. The annular internal wall62and larger included portion45interface establishes the linear distance that the first end42of the spool-spindle34is spaced from the first plane defined above. The annular internal wall62and larger included portion45interface also establishes the concentric alignment of the first end42of the spool-spindle34within the case32. As one of the advantages of the invention, the alignment within the case32is accomplished without washers. For further mechanical stability, in one of the preferred embodiments, the spool opening(s)46allows potting epoxy38to be introduced into the case32. This enables potting compound38to fill spaces or voids defined between the spool-spindle34and the conductors31, between the conductors31and the case32, and between the individual conductors31, as shown inFIG. 2. Upon curing, the potting compound38robustly joins the internal components of the electromagnetic coil assembly30and fixes them in place.

The case32and the spool-spindle34can be made of magnetically conductive materials. Also, the spool-spindle34can be made with a lathe machine (not shown). Lathe machines and the use of lathe machines to make turned parts and components are well known to those having ordinary skill in the art.

As noted above, in another embodiment the spool-spindle34may be joined to the case32by crimping, and this is shown inFIG. 9. For this purpose, an annular internal lip80is provided on casing internal surface60near end face56. The spool spindle34is moved into the case32in the above-described manner and the lip80that surrounds the second case end56is crimped as shown inFIG. 9. This joins the spool-spindle34and the case32as shown inFIG. 9. Crimping increases the degree to which the case32and the spool-spindle34are joined to one another. As a result, less reliance needs to be placed on the potting epoxy38that is also used to join the spool-spindle34to the case32.

In other embodiments, the annular internal wall or shoulder62may be eliminated if a fixture (not shown) is used to hold the case32and spool-spindle34together so that they can be joined together with a weld. In another embodiment, the annular internal wall62is eliminated, and fixturing may be employed as well as a locator to fix the location or position of the spool-spindle34relative to the case for the process that introduces the means for fastening, such as epoxy38. The locator may then be removed or remain part of the coil assembly.

In another embodiment a step or shoulder may be machined into the larger included portion45. Then a portion of the peripheral surface39of portion45may be received in the open region58in the second end56of the case32, but the remainder of the peripheral surface39of the larger included portion45cannot be received in the open region58in the case, due to engagement between the step or shoulder of portion45and the annular end surface56of the case32. In such an embodiment, the annular internal wall62may or may not be present, because the introduction of the spool-spindle34into the case32is controlled by the shoulder formed in the larger included portion45.

The electromagnetic coil assembly30employing the above-described spool-spindle34has a number of advantages. Some of the advantages are that fewer components need to be manufactured, assembly steps are eliminated, fixturing is eliminated, and dimensional accuracy of the final assembly is easier to control because there are fewer component interface locations. More advantages include the elimination of the washer component from the manufacture and assembly process, optional use of the locater component, the immediate constraining of the spool-spindle34upon its insertion into the case32, and elimination of the washer-spindle interface. Another advantage is that the positions of the spool-spindle34and case32are easier to control via the dimensions and tolerances used to manufacture the spool-spindle34and case32. In addition, another possible advantage is that the continuity of the magnetic lines of force may be improved by the structure of the spool-spindle thereby possibly improving the performance of the electromagnetic coil.

FIG. 10shows the electromagnetic coil assembly30in a low power electromagnetic pump100which, for example, can be used in implantable drug delivery systems. In the arrangement shown, coil assembly30is axially adjacent the pump housing102which contains an armature/plunger (not shown) which is magnetically influenced by coil assembly30to pump fluid from an inlet104connected to a supply reservoir (not shown) to an outlet106to a point of use for the fluid. Pulsed operation of coil assembly30by an appropriate electrical circuit (not shown), typically battery-operated, causes reciprocating operation of the pump armature/plunger which is typically spring biased. For a more detailed description of such an electromagnetic pump, reference may be made to the previously mentioned U.S. Pat. No. 6,264,439 issued Jul. 24, 2001, the disclosure of which is hereby incorporated by reference.

It will be appreciated by those skilled in the art that while the invention for electromagnetic coil assembly employing a spool-spindle has been described above in connection with particular embodiments and examples, the invention is not necessarily so limited and other embodiments, examples, uses, and modifications and departures from the embodiments, examples, and uses may be made without departing from the invention. All of these alternative embodiments are intended to be within the scope and spirit of the this invention.