Expanding the Use of Hypothetical Analysis When Evaluating Patent Infringement Under the Doctrine of Equivalents

Publication year1993


Expanding the Use of Hypothetical Analysis When Evaluating Patent Infringement Under the Doctrine of Equivalents

Brian E. Lewis (fn*)

I. Introduction

A patent is a grant to exclude others from making, using, or selling a claimed invention without the patent holder's permission.(fn1) The patent holder has the right to bring a civil action when she believes her patent has been infringed.(fn2) Defining the limits of a patent holder's right to exclude others from making, using, or selling the patented invention, however, has proved to be a formidable task. Early in American patent history, an equitable doctrine was established to provide a patent holder with a remedy against items that were practically, but not quite exactly, identical to the claimed invention.(fn3) This has become known as the doctrine of equivalents. The doctrine of equivalents method evaluates whether an item infringes on a patent when it is not precisely covered by the express language of the patent but is substantially the same.

The equitable nature underlying the doctrine of equivalents can be illustrated by a simple example. Imagine a world without paper clips of any sort. One day our hero, John Clip, while idly sitting at his desk, wraps a short length of wire around an eraser. The wire eventually drops from the eraser next to a stack of paper catching several pages together and Eureka! the paper clip is invented. Mr. Clip's patent claim reads: "I claim-A non-invasive paper fastening device comprising a piece of metal wire having three 180 U-bends, said bends all lying in a single geometric plane."

Much to his distress, Mr. Clip's financial success from the paper clip is undermined by Ms. Shiphty who, appreciating the commercial potential of the paper clip, sets out to manufacture an imitation that just avoids the patent claim language. She flanges the ends of the paper clip outward slightly, thus avoiding the "one plane" limitation of the patent. Mr. Clip cannot argue that Ms. Shiphty's device is exactly what he claimed because, in patent parlance, her device does not "read on" his patent.(fn4) Mr. Clip's right to exclude is so narrow that he will lose the benefit of his invention because Ms. Shiphty marginally circumvents the patent claim's express language. The doctrine of equivalents attempts to avoid such abuse of patent rights.(fn5)

Despite the obvious inequities involved in this example, the edges of the doctrine of equivalents are defined by closer cases, and the doctrine is frequently clarified by the Federal Circuit.(fn6) Among the more recent decisions attempting to clarify application of the doctrine of equivalents is Wilson Sporting Goods v. David Geoffrey and Assocs.(fn7) Wilson proposed that a court evaluating infringement under the doctrine of equivalents should conceive a hypothetical version of the patent at issue, which expands the patent claim enough so that the allegedly infringing device reads on the patent claim.(fn8) If this expanded version of the claim would also cover prior art,(fn9) the doctrine of equivalents would be stretched too far to find infringement. This hypothetical technique for evaluating the effect of prior art on any doctrine of equivalents infringement has been useful,(fn10) but the hypothetical could be even more useful.

Accordingly, the purpose of this Comment is twofold: first, to bring the reader up-to-date on the doctrine of equivalents, and second, to suggest an improvement on the doctrine's application that is consistent with recent developments. This Comment proposes that the hypothetical technique should be expanded to evaluate more than prior art alone. Before exploring how this new use of the hypothetical would work, however, it is necessary to explain the doctrine of equivalents' history, the factors that affect the range of equivalents, and the methods to determine and apply equivalents.

II. Origin of the Doctrine of Equivalents

The doctrine of equivalents appeared in the United States over one hundred years ago,(fn11) and the United States Supreme Court first applied the doctrine in Winans v. Denmead.(fn12) In that case, the Court held that the infringer's octagonal-shaped coal car was equivalent to the patented cone-shaped coal car because it performed the same novel functions as the patented car even though it did not literally infringe on the patent claims.(fn13) The dissent in Winans, however, feared that to allow a finding of infringement where the allegedly infringing item does not read on the patent, but misappropriates the underlying idea, would be to cause judicial unpredictability.(fn14)

While Winans marked the Court's legitimization of the doctrine of equivalents, the Court's most noted application of the doctrine was in Graver Tank and Manufacturing v. Linde Air Products Co.(fn15) In that case, the Court evaluated the alleged infringement of a patent for a welding flux.(fn16) The patent at issue claimed a combination of materials including magnesium. The allegedly infringing welding flux was identical to the patented flux except that manganese was used in place of magnesium.(fn17) The Court held that the patent was infringed because persons skilled in the art would know that manganese was equivalent to and could be substituted for magnesium.(fn18) Graver Tank is noteworthy because, in coming to its decision, the Court set out an evaluation standard that has become the essence of every doctrine of equivalents analysis and because it provided a precedent for seeking to satisfy the equitable policy underlying the doctrine. That standard provides: "[A] patentee may invoke [the doctrine of equivalents] against the producer of a device if it performs substantially the same function in substantially the same way to obtain the same result."(fn19)

The policy set out in Graver Tank underlies much of the subsequent evolution of the doctrine of equivalents. The Court recognized that the doctrine's equitable nature would prevent the application of any brightline rule.(fn20) Therefore, the Court relied on policy, stating that the doctrine is necessary "to temper unsparing logic and prevent an infringer from stealing the benefit of an invention."(fn21) Similarly, the Court added that "to permit imitation of a patented invention which does not copy every literal detail would be to convert the protection of the patent grant into a hollow and useless thing."(fn22)

Graver Tank, however, was not a unanimous decision. Two justices found the policy against allowing use of the doctrine of equivalents more persuasive. Justice Douglas argued that the majority used the doctrine of equivalents to expand the original patent to a welding flux that would have been made obvious and thus unpatentable by the prior art.(fn23) Justice Black argued that Graver Tank was an improper place for applying the doctrine of equivalents because: (1) the patentee was seeking broader protection than claimed in his patent, and (2) the majority's holding failed to "protect[ ] businessmen from retroactive infringement suits and judicial expansion of a monopoly sphere beyond that which a patent expressly authorizes."(fn24)

In spite of such arguments, both Winans and Graver Tank used the doctrine of equivalents to achieve results that would give patent protection meaningful breadth. The Court's primary objective in each case was to encourage inventions by discouraging narrow avoidance of a patent's language.(fn25)

III. Limitations on the Permissible Range of Equivalents

Four sources of information limit the range of equivalents that a patentee may be allowed to obtain: the patent, the prosecution history of the patent,(fn26) the prior art related to the patent, and the degree to which the invention is of a pioneering nature.(fn27)

A. The Patent and Prosecution History

A court should begin an infringement analysis by looking at the face of the patent.(fn28) The patent claim defines the literal limits of what the patent holder may exclude others from making, using, or selling. Claim construction is a matter of law for the court to decide.(fn29) A patent also has a specification that describes the invention and methods for making it and using it. The patent specification is secondary to the claim, and while it may help a court understand what is claimed, it cannot be the basis for limiting the range of equivalents.(fn30) The patent claim and patent specification work together to define the maximum range of equivalents. Only after a court interprets the patent, concludes that no literal infringement exists, and determines that finding the patent not infringed may be unfair to the patentee, may the court evaluate the patent under the doctrine of equivalents.(fn31)

Under this doctrine, a court should first look to the patent's prosecution history.(fn32) Prosecution history is the history of a patent's evolution from the first version of the patent submitted to the Patent and Trademark Office (PTO) to the patent as issued.(fn33) Where the patentee has made concessions to the patent examiner in the way of restrictions in language of claims to obtain the patent, these concessions or restrictions may be used to limit the patentee.(fn34) In particular, in a subsequent infringement action, the patentee is prevented or estopped from asserting claim interpretations that encompass the...

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