United States: Intrinsic Record Must Contain an Explicit Definition or Disavowal to Avoid Adopting the Plain and Ordinary Meaning of a Disputed Claim Term

Continuing an almost two-year long trend, the U.S. Court of Appeals for the Federal Circuit found that the district court crossed a fine line between "reading a claim in light of the specification, and reading a limitation into the claim from the specification." Liquid Dynamics v. Vaughn Co., Case Nos. 03-1146, -1147, -1208 (Fed Cir. Jan. 23, 2004).

The patent-in-suit describes a tank that stores liquid and semisolid waste products and mixes the waste products for subsequent processing. As recited in the asserted claims, the tank mixes the waste products by generating a "substantial helical flow path." The parties disputed the scope of the phrase "substantial helical flow" and "substantially helical flow path." The defendant advocated that each term required a geometrically helical pattern.

The district court observed that the phrase "substantial helical flow path" was ambiguous and, therefore, looked to the specification and the prosecution history to construe its scope. The figures included in the specification only illustrated a perfect helical flow path. In addition, during prosecution, the applicant differentiated the claimed invention from prior art that had a generalized helical flow path. Based on these representations, the district court construed the recited term to "require a perfect helical flow path." Liquid Dynamics appealed.

The Federal Circuit reversed, outlining the steps required for proper claim construction and noting that "[a]s the starting point, [the Court should] give claim terms their ordinary and accustomed meaning as understood by one of ordinary skill in the art." The Court further emphasized that unless the specification acts as a dictionary and expressly defines the claim term or the patentee unequivocally disavows a certain meaning during prosecution, the plain and ordinary meaning of the claim term prevails.

The Federal Circuit found that the disputed claim term "was not ambiguous and its plain meaning was not contradicted by the written description." "Because the plain language of the claim was clear and uncontradicted by anything in the written description or the figures, the district court should not have relied upon the written description, the figures, or the prosecution history to add limitations to the claim." Accordingly, the Federal Circuit focused on the ordinary meaning of the term "substantial" and held that the proper construction for disputed phrase permitted the flow path to have a general rather than a perfect spiral pattern.