“Substantially” in a Patent Claim is Substantially OK

U.S. Patent No. 5,987,863 ("the ‘863 patent”), owned by the Exmark Manufacturing Company (“Exmark”), recently survived a challenge to its claim 1 as indefinite under 35 U.S.C. §112, ¶2 for inclusion of the phrase “elongated and substantially straight.”  The United States Court of Appeals for the Federal Circuit (“the Federal Circuit”) affirmed a refusal by the United States District Court for the District of Nebraska to grant summary judgment on a motion alleging the invalidity of claim 1 of the ‘863 as indefinite under 35 U.S.C. §112, ¶2.  The motion was made by Briggs & Stratton Power Products Group, LLC’s (“Briggs & Stratton”) in an infringement action initiated by Exmark against Briggs & Stratton.  EXMARK MANUFACTURING COMPANY INC., Exmark Manufacturing Company Inc. (Plaintiff-Appelee) v. Briggs & Stratton Power Products Group, LLC (Defendant-Appellant), 2016-2197 (January 12, 2018).

The Federal Circuit looked for evidence that claim 1 “. . . when read in the light of the specification, informs those skilled in the art of the scope of the ‘elongated and substantially straight‘ limitation with reasonable certainty.”  The Federal Circuit cited the Supreme Court decision in Nautilus, Inc. v. Biosig Instruments, Inc., 134 S. Ct. 2120, 2129 (2014):

“Pursuant to 35 U.S.C. § 112, ¶ 2, a patent specification must ‘conclude with one or more claims particularly pointing out and distinctly claiming the subject matter which the applicant regards as his invention.’ A claim is indefinite if, when read in light of the specification and prosecution history, it fails to inform those skilled in the art about the scope of the invention with reasonable certainty.”

A key part of the claim reads (emphasis added):

“said first flow control baffle comprising a first arcuate baffle portion, having first and second ends, which extends from the interior surface of said second side wall partially around said first cutting blade, a first elongated and substantially straight baffle portion, having first and second ends, extending from said second end of said first arcuate baffle portion, a second arcuate baffle portion, having first and second ends, which extends from said second end of said first elongated and substantially straight baffle portion partially around said second cutting blade;

said first elongated and substantially straight baffle portion being angularly disposed with respect to the said circle defined by the blade tip path of said second cutting blade in a chord-like fashion so that the cuttings from said first cutting blade will be deflected inwardly within the said circle defined by the blade tip path of said second cutting blade.”

In its analysis, the Federal Circuit looked both collectively and separately at “elongated” and “substantially straight” to determine if the terms could be understood by one skilled in the art.

In considering the limitations collectively, the Federal Circuit noted that the “elongated and substantially straight baffle portion” did not stand by itself.  It is defined in part by its relationship with other elements in the claim, e.g., first and second arcuate baffle portions, allowing one skilled in the art to determine a proportional length of an “elongated and substantially straight” baffle portion based on the size of the other lawnmower components.  The Federal Circuit determined that “. . . the claims and specification provide that the elongated and straight portion of the baffle must be long enough and straight enough to at least connect these two arcuate portions of the baffle.”

In assessing the definiteness of “elongated,” the Federal Circuit contrasted the present case with an earlier non-precedential case, identified by Briggs & Stratton, in which “elongated” was found to be indefinite.   In that earlier case, the Federal Circuit “found nothing in the patent at issue provided any objective boundaries for the term ‘elongated.’” That was contrasted with the ‘863 patent, which “provide[s] information to objectively define the scope of the ‘elongated’ claim term.”  The Federal Circuit did not require a precise length for “elongated,” determining a proportional length, as limited by the language of the claims, to be sufficient.

Regarding the “substantially straight” limitation, Briggs and Stratton sought “. . . to impose a strict requirement of how straight the baffle portion must be.”  However, the Federal Circuit disputed the need for the establishment of such a strict requirement, stating “. . . no such numerical precision is required when using such terms of degree.  See Sonix Tech. Co. v. Publ’ns Int’l, Ltd., 844 F.3d 1370, 1377 (Fed. Cir. 2017).“  The Federal Circuit concluded that “. . . one skilled in the art would understand that the ‘substantially straight’ portions of the baffle must be sufficiently straight to connect two arcuate portions of the baffle.” 

The Federal Circuit affirmed the district court’s decision to reject the motion for summary judgment, stating: “We agree with the district court that the claim language and specification of the ’863 patent provide reasonable certainty as to the meaning of ‘elongated and substantially straight.’”

Lessons for Practice

  1. When using “substantially” in a claim, provide sufficient limitations in the claims and support in the spec to allow one skilled in the art to reasonably determine, for example, how straight is straight enough.   
  2. Don’t be afraid of functional language when using “substantially,” but do be aware of the potentially narrow reading of the claims. A narrower reading may be the trade-off for reasonable certainty. 

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