Deciphering Means-plus-function Claim Limitation Infringement Under § 112, Paragraph 6: Finding Certainty in the Uncertain Case Law

• Publication year: 2001
• Citation: Vol. 3 No. 2001

Chad S.C. Stover⁰

I. Abstract

The development of a technology-centered economy has increased the importance of patent rights. In order for these patent rights to have value, patentees must be able to ascertain the metes and bounds of their patent claims. In recent years the Federal Circuit has muddled means-plus-function claim limitation infringement analysis governed by 35 U.S.C. § 112, ¶ 6. Because the Federal Circuit uses different approaches to decide claims, it has become impossible to know the metes and bounds means-plus-function (MPF) limitations create.

For example, in two recent cases, Kemco Sales, Inc. v. Control Papers Co., Inc. and IMS Technology, Inc. v. Haas Automation, Inc., the Federal Circuit has used divergent approaches to analyze MPF claim limitation infringement. In Kemco, the court used the narrow approach to § 112, ¶ 6 infringement analysis, focusing on the structural equivalence of the accused structure to the patented structure. In IMS, the court used the contextual approach to infringement, looking at the claim limitation's position in the context of the overall invention. This inconsistency unjustly forces inventors to rely on litigation to decide the scope of their patents' rights to exclude.

In order to promote innovation, the more logical interpretation of 35 U.S.C. § 112, ¶ 6 is a narrow approach focusing on a simple structural equivalence comparison. This Comment shows the benefits of the narrow approach over the more complicated contextual approach.

II. Introduction and Background

As technology develops at the center of an interdependent world economy, the importance of the patent as a means to carve out a part of this new economy increases. Patent claims define the metes and bounds of an invention, thereby defining the scope of patent protection and determining the worth of the right to exclude granted by the patent. Patent claims written in "means-plus-function" or "step-plus-function" format (hereafter "MPF format") define a claim limitation by what it does rather than by its structure.¹

The MPF format may provide advantages over ordinary structural claims for certain types of inventions. MPF language is generally used where the function or action, rather than the specific structure that accomplishes the action, is important.² 35 U.S.C. § 112, ¶ 6 governs MPF claim limitations.³ MPF format incorporates into the limitations of the claim the embodiment disclosed in the specification and all of its equivalents, provided there is a clear link in the specification or prosecution history between the function recited in the claim and a particular structure in the disclosure.⁴ In order to broaden the scope of means limitations, the claim drafter should expressly recite various alternative structural features corresponding to the means limitation.⁵ Means limitations place on the drafter a burden to draft a broad specification.⁶

Section 112, ¶ 6 was enacted as part of the Patent Act of 1952, likely in response to Halliburton Oil Well Cementing Co. v. Walker⁷ Halliburton forbade the use of MPF language at the point of novelty because the Court thought MPF elements were overbroad and ambiguous.⁸ Perhaps in response to Halliburton, Congress enacted § 112, ¶ 6 as part of the Patent Act of 1952, permitting the use of MPF language but providing "a standard to make the broad claim language more definite."⁹ The words of the statute read:

An element in a claim for a combination may be expressed as a means or step for performing a specified function without the recital of structure, material, or acts in support thereof, and such claim shall be construed to cover the corresponding

structure, material, or acts described in the specification and equivalents thereof.¹⁰

Apparent from this language, the purpose of § 112, ¶ 6 is to grant the inventor a fair scope that is not dependent on a catalogue of alternative embodiments in the specification.¹¹ In addition to granting a fair scope to patent grants, there is some evidence to support the hypothesis that Congress intended § 112, ¶ 6 to codify the application of the judicially-created doctrine of equivalents to MPF claim limitations.¹² Unfortunately, as this Comment will show, the interpretation of the statute has not provided the definiteness anticipated by its drafters.¹³ Uncertainty over the legislative intent of § 112, ¶ 6 exists; the interpretation of § 112, ¶ 6 that the plain meaning of the statute is a codification of the doctrine of equivalents has been both accepted and rejected.¹⁴ This Comment will argue that the plain meaning of the statute rightly should separate the doctrine of equivalents and the § 112, ¶ 6 inquiries.

The Federal Circuit has developed a general test for MPF claim literal infringement under § 112, ¶ 6. Provided all other limitations of a claim are literally met, an accused structure is said to literally infringe a MPF claim limitation if two elements are present: (1) the accused infringing structure contains the equivalent structure to that disclosed in the section of the specification corresponding to the MPF limitation,¹⁵ and (2) the relevant structure in the accused infringing device and the structure in the corresponding specification perform the identical function and are insubstantially different from the MPF limitation.¹⁶

Doctrine of equivalents non-literal infringement developed in the common law as a way to protect the substance of a patentee's right to exclude when literal infringement fails. It does so by ensuring that merely colorable differences or slight improvements beyond the literal scope of a claim do not prevent infringement.¹⁷ The Federal Circuit in Kraft v. International Trading Co. stated:

Equivalence is shown by evidence that the accused device contains an element that is not "substantially different" from any claim element that is literally lacking ... or that the claimed limitation and the accused component "perform substantially the same function in substantially the same way to achieve substantially the same result."¹⁸ Under the tripartite function/way/result test of the doctrine of equivalents, the fact finder must consider factors such as the prosecution history, the pioneer-non-pioneer status of the invention, and the prior art to make a determination of infringement. Determination of the importance of the limitation to the invention as a whole, often referred to as whether the limitation is at the "point of novelty," also has been used as a factor in doctrine of equivalents infringement determinations.¹⁹

Even though § 112, ¶ 6 and the doctrine of equivalents seem very similar, there are significant differences between the two inquiries. Equivalence analysis under § 112, ¶ 6 is essentially the application of the doctrine of equivalence in a limited role.²⁰ § 112, ¶ 6 analysis uses the same tripartite function/way/result test of the doctrine of equivalents, but § 112, ¶ 6 literal infringement stresses functional identity, not equivalency.²¹ Thus, § 112, ¶ 6 equivalence is narrower than the doctrine of equivalents.²²

In addition, there is a temporal distinction between the statutory and common law equivalence inquiries.²³ The literal meaning of a claim fixes upon issuance, and, as such, equivalence analysis under § 112, ¶ 6 only can concern technology in existence at the time of issuance.²⁴ As Donald Chisum states in his treatise, however, "if the accused technology was developed after the patent issued, infringement exists, if at all, under the common law doctrine of equivalents. In short, a threshold determination must be made as to when the technology embodied in the accused product was available—pre- or post-issuance."²⁵

Following from this, doctrine of equivalents analysis is precluded for MPF limitations after a § 112, ¶ 6 finding of no literal infringement if the technology of the accused device existed at the time of patent issuance.²⁶ The courts never have held that § 112, ¶ 6 codified the doctrine of equivalents, but the courts' struggle to define the differences has led to confusion in MPF claim limitation infringement as illustrated in the following cases.

III. Case Summaries

A. Kemco Sales, Inc. v. Control Papers Co.²⁷

Kemco owns U.S. Patent 5,405,197 for plastic security envelopes.²⁸ The envelopes indicate whether the envelope has been opened and has had its valuables removed. Previous envelopes considered as prior art were not secure because the adhesive securing the flaps could be heated, the contents could be read, and the adhesive could be reapplied without any indication that the envelope had been opened.²⁹ Kemco's new envelope utilizes two sealing means. One sealing means is extremely temperature sensitive to show tampering, and the other sealing means physically seals the envelope.³⁰

Control Papers also made a security envelope. This accused infringing envelope also utilized two adhesive layers. The only difference in Control Papers' accused infringing envelope was its use of a dual-lip structure rather than the single-lip structure disclosed in Kemco's patent.³¹

Kemco sued for infringement in United States District Court for the District of New Jersey. The district court granted partial summary judgment in favor of Control Papers. Kemco appealed, placing the infringement determination in the hands of the Court of Appeals for the Federal Circuit.³²

After determining the meanings of various phrases in the patent, the court began the infringement analysis relevant to this discussion. The court stated that a two-pronged test governed the analysis. First, the accused infringing product must have identical function to the disclosed structure in the patent. Second, the accused infringing product must be otherwise insubstantially different with respect to structure.³³ The court advocated the modified function/way/result test partially borrowed from doctrine of equivalents analysis.³⁴

The court said a key difference between the § 112, ¶ 6 infringement analysis...