Festo Corporation v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd.

535 U.S. 722 (2002)

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Nature of the Case

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Facts

P owns two patents for an improved magnetic rodless cylinder, a piston-driven device that relies on magnets to move objects in a conveying system. P's patent applications were amended during the prosecution proceedings. The '125 patent was amended after the patent examiner rejected the initial application because the exact method of operation was unclear and some claims were made in an impermissible way. A new application designed to meet the examiner's objections was submitted which also added certain references to prior art. The '401 patent was also amended during a reexamination proceeding and prior art references were added to this amended application. Both amended patents added a new limitation -- that the inventions contain a pair of sealing rings, each having a lip on one side, which would prevent impurities from getting on the piston assembly. The '125 Patent added a further limitation that the outer shell of the device, the sleeve, be made of a magnetizable material. D entered the market with a device similar, but not identical, P's. D's cylinder employs a single-sealing ring with a two-way lip. D's sleeve is made of a nonmagnetizable alloy. D's device does not fall within the literal claims of either patent. P contends that it infringes under the doctrine of equivalents. D invoked prosecutorial estoppel and contends that P is estopped because of the prosecution history of its patents. The sealing rings and the magnetized alloy in the P product were both disclosed for the first time in the amended applications. D claims that P is now estopped from saying that these features are immaterial and that D's device is an equivalent of its own. The Court held that P's amendments were not made to avoid prior art, and therefore the amendments were not the kind that give rise to estoppel. A panel of the Court of Appeals for the Federal Circuit affirmed. The Supreme Court granted certiorari, vacated, and remanded in light of Warner-Jenkinson. After a decision by the original panel on remand, the Court of Appeals ordered rehearing en banc to address questions that had divided its judges since Warner-Jenkinson. The en banc court reversed, holding that prosecution history estoppel barred P from asserting that the accused device infringed its patents under the doctrine of equivalents. It held that estoppel arises from any amendment that narrows a claim to comply with the Patent Act, not only from amendments made to avoid prior art. It held that when estoppel applies, it stands as a complete bar against any claim of equivalence for the element that was amended. The dissenters argued that the majority's decision to overrule precedent was contrary to Warner-Jenkinson. The Supreme Court again granted certiorari.