Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd. Case Brief Summary | Law Case Explained

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Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd. | 535 U.S. 722 (2002)
The doctrine of equivalents and prosecution-history estoppel are two long-standing principles of patent law. In Festo versus Shoketsu Kinzoku Kogyo Kabushiki, the United States Supreme Court considered the interaction of the two doctrines.
Festo owned two patents for a magnetic rodless cylinder. Both patents were initially rejected and then amended during the reexamination proceedings. Both patents added a new limitation, that the device has a pair of sealing rings, each having a lip on one side, to prevent impurities from entering the piston mechanism. The first patent also added that the device’s sleeve be made of magnetizable material.
Shoketsu Kinzoku Kogyo Kabushiki Corporation, also known as SMC, began selling a similar device. However, SMC’s device used a single sealing ring with a two-way lip and a sleeve made of a non-magnetizable alloy.
Festo sued SMC for patent infringement, arguing that SMC’s device infringed under the doctrine of equivalents. SMC argued that Festo was estopped from asserting the doctrine of equivalents because Festo had narrowed its patent claims during the application process.
The district court ruled for Festo and the Court of Appeals for the Federal Circuit affirmed. The Supreme Court granted cert, vacated, and remanded the case in light of its intervening decision in Warner-Jenkinson versus Hilton Davis Chemical. On remand, the Federal Circuit reversed, ruling for SMC. The Supreme Court granted cert.
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