Lawn mower found to infringe on patent. EXMARK MFG. v. BRIGGS & STRATTON

Lawn mower found to infringe on patent. EXMARK MFG. v. BRIGGS & STRATTON

A patent is a set of exclusive rights granted to the inventor of an invention that meets certain criteria. A patent grants its owner the exclusive right to make, use, sell and import the invention claimed in the patent.  If someone other than the patent owner attempts to exercise on of these exclusive rights, that is considered patent infringement.  To combat patent infringement a patent owner can file a complaint in United States Federal Court.

There are two types of infringement: (1) Direct infringement – The accused infringer practices each element of the patent holder’s patent claim and (2) Indirect infringement – The accused infringer does not practice each element of the patent holder’s patent claim but either: (a) contributes to direct infringement by another party or (b) induces another party to engage in direct infringement.  To prevail on a patent infringement claim, a patent owner must
show by a preponderance of the evidence that each asserted patent claim limitation is found in the accused product or process, either: (1) Literally or (2) Under the doctrine of equivalents

Patent claims may be written in English, however the words in the claims do not always match their dictionary definition.  A patent infringement case typically turns on how a court interprets the claims of a patent in a Markman hearing.  The written description, the drawings, and the prosecution history are all evidence used to interpret the claims of a patent. The claims are interpreted from the perspective of a person having ordinary skill in the art (PHOSITA).  A PHOSITA is a hypothetical person that is familiar with the technology that the invention is related.  The PHOSITA is deemed to read the claim term not only in the context of the particular claim in which the disputed term appears, but in the context of the entire patent, including the specification.

The ultimate construction of a claim term is a legal question reviewed de novo, while underlying factual determinations made by the district court are reviewed for clear error.

EXMARK MFG. CO. v. BRIGGS & STRATTON CORP. 19-1878 (C.A.F.C. 2020) is a case which illustrates the importance of claim construction to a patent infringement case.

This case began in 2011 when Exmark filed a patent infringement suit against Briggs in 2010 alleging infringement of certain claims of U.S. Patent No. 5,987,863. The invention claimed in the ’863 patent relates to lawn mowers, and specifically to the use of baffles to control and guide the flow of air and grass clippings through the mower.

Defendant argued that the claim language of the ‘863 patent was indefinite, but the district court was not persuaded by this argument.  The district court determined that the claim language of the ‘863 patent required some spatial separation between the first flow control baffle and the front wall, and the claimed “discharge opening” was not met by a prior art “opening” that was obstructed.  Based on this finding that the ‘863 patent was valid the District court entered summary judgement in favor of the Plaintiff.

Defendant appealed the district court’s orders (1) granting summary judgment of no invalidity; (2) denying summary judgment of indefiniteness; (3) granting summary judgment of infringement; and (4) computing prejudgment interest to the Court of Appeals for the Federal Circuit.

On appeal the Federal Circuit noted that claim construction is a question of law.  A district court judge’s claim construction results in a determination of law which is reviewed de novo on appeal.  In the case at hand the Federal Circuit found that the ‘863 patent did not require spacial separation between the flow control baffle and the front wall.

Even though the Federal Circuit vacated the district court’s construction of “flow control baffle”that required spatial separation with the front wall, the Federal Circuit found that summary judgment of infringement was appropriate regardless of whether “flow control baffle” is construed to require spatial separation.  The court based this conclusion on a simple comparison between the diagrams of the ‘863 patent and the allegedly infringing device, which is reproduced above.

Based on these conclusions the Federal Circuit affirmed the District Court’s finding of validity and infringement.

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