Six years ago, in Festo Corp. v. Shoketsu Kinzoku Kogyo Kabashiki Co., 535 U.S. 722 (2001), the Supreme Court considered how changing a patent application during its prosecution limits later claims of infringement under the doctrine of equivalents. The Court held that amendment of the Festo application didn’t necessarily preclude infringement by Shoketsu’s device and remanded for further proceedings.
More proceedings ensued and resulted, after a bench trial, in a judgment of non-infringement because, the district court found, a person of ordinary skill in the art would have foreseen the Shoketsu equivalent at the time of the amendment. The Federal Circuit affirmed, holding that an amendment precludes a claim of infringement by an equivalent device that "is known in the prior art at the time of the amendment." Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd., No. 05-1492 (Fed. Cir. July 7, 2007).