Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1998-12-21
2001-04-24
Gerrity, Stephen F. (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C264S272150, C264S272190, C343S895000
Reexamination Certificate
active
06219902
ABSTRACT:
The present invention generally concerns a method for manufacturing a protectively coated helically wound antenna, such as those typically used in portable communication devices. More specifically, the present invention concerns a method for manufacturing a helically wound antenna which forms the protective coating using injection molding, but avoids deformation of the helical winding during molding by precise and repeatable control of the molding point relative to the winding.
BACKGROUND OF THE INVENTION
Portable communicators, such as cell phones, frequently utilize antennas including a helical winding. Helical windings permit a relatively long effective antenna length with a small physical antenna length. This is convenient in cell phones and other portable communicators since small physical size is beneficial and since a certain antenna length is necessary to achieve particular broadcast and reception frequencies. Accordingly, antennas are frequently formed, in whole or part, from a helical conductor. Small size also dictates that the wire used to form the helical conductor be thin. This requires the helical conductor to be encased in a protective material, since cell phone antennas are often subjected to forces which would permanently deform delicate helical windings.
The typical helical windings are formed from a thin and delicate conductive wire. Thin wires help preserve the desired small size and low weight which is desirable in portable communicators. Thin conductive wires also facilitate the low power transmission and reception functions of portable communicators.
The coating of such thin helical conductors with protective material has proved difficult. Injection molding is an efficient and widely used coating technique, but often deforms delicate helical antenna conductors. The helical winding is placed in a mold, typically while it is mounted on a core, and thermoplastic material is injected into the mold. Significant forces are applied to the helical winding during the injection, and deform the winding by changing its pitch, i.e., the spacing between windings, and causing the pitch to be nonuniform. This changes the electrical characteristics of the antenna in a manner which may vary from one antenna to the next during manufacturing. Compensation for these variances is often achieved through additional processing, such as testing and trimming to tune the antenna to a desired frequency. Even still, a significant percentage of manufactured antennas may be unsuitable for use. Obviously, this increases both the cost and difficulty of manufacturing. In addition, performance tolerances must be generous enough to accommodate the variances experienced in those antennas which are still suitable for use.
It is known to wind the helical structure around supports prior to injection to attempt to avoid deformation. Exemplary techniques are disclosed in Bumsted, U.S. Pat. No. 5,648,788, Jul. 15, 1997, and in Valimaa et al., U.S. Pat. No. 5,341,149, Aug. 23, 1994. In the first technique, a relatively complex molding process is disclosed, where a sliding bar locks a coil onto a special handle assembly for molding. The mold includes mold pads for holding the coils in place during molding. This leaves portions of the coils exposed, requiring additional processing.
Valimaa also recognizes the potential for thin helical windings to deform during injection molding, and discloses a threaded support core, used for molding of helical coils. The core is completely molded into the coil and therefore cannot control the point of injection relative to the beginning of the winding. Neither Bumsted or Valimaa recognizes or addresses the need to control this point to avoid deformation in the first few windings.
In sum, there is a need for an improved and efficient method of manufacturing a protectively coated helically wound antenna which addresses shortcomings of prior techniques. In addition, there is a need for an improved and efficient method for manufacturing such an antenna which produces a repeatable consistent helical structure, avoids deformation throughout the winding, and avoids significant post-processing trimming and tuning.
SUMMARY OF THE INVENTION
The present method is an improved, efficient and repeatable method for manufacturing a protectively coated helical conductor antenna. The helical conductor is threaded onto a temporary, removable support, such as a bolt including an asymmetrically shaped head and a shank having threads to hold the helical conductor. After being threaded on the shank, the entire winding and the associated portion of the bolt shank are placed within an injection mold cavity. The mold also preferably includes a recess outside of the injection cavity for accommodating the bolt head, with the recess being shaped to permit a specific orientation for the bolt. The shape of the bolt head and the recess define a repeatable orientation for the bolt and helical conductor. As a result, the point of injection relative to the helical winding may be exactly repeated time and time again. This allows selection of an injection point relative to the helical winding that produces minimal deformation, and the obtainment of consistent results thereby reducing variation and necessary manufacturing tolerances
A preferred application of the present method is manufacture of an antenna having an elongated conductor, with a helical conductor attached at an end of the elongated conductor. The helical conductor and elongated conductor are joined by an electrode. A shank end of the bolt mates with the electrode and presses against the beginning of the helical winding. The shaped head of the bolt orients the beginning of the helical winding, which is locked between the electrode and shank, adjacent the thermoplastic injection point. Pressing of the bolt at this point prevents deformation of the helical winding at the point where the force created by thermoplastic injection is most powerful, while the shank threads oppose deformation of the helical winding throughout its remainder.
After injection, the mold is opened, and the bolt and antenna are removed. Because the head was kept outside of the injection cavity, the bolt is conveniently removed by unthreading. An opening left where the bolt was removed may be capped. A core may be inserted in the space occupied by the shank during the injection molding. Alternatively or additionally, center fill molding may be used to finish the open end.
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Memmen Stephan D.
Schneiderman Douglas
Gerrity Stephen F.
Greer Burns & Crain Ltd.
Sands Rhonda E
T & M Antennas
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