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Prosecution history estoppel, also known as file-wrapper estoppel essentially means that when an inventor during prosecution narrows down his invention to escape prior art by some amendment, then he cannot claim that someone else infringed his patent under doctrine of equivalence (DOC). Amendment to the patent claims and argument by the patentee during the patent application process may limit the range of equivalents to which patentee is later entitled under the DOC.

The prosecution history estoppel is invoked to prevent the application of the doctrine of equivalents where claim scope has been surrendered either by express disclaimer or by narrowing amendment. The scope of application of prosecution history estoppel to this latter category has been the subject of much debate in the US patent bar.

One of the famous case that examined the relationship between doctrine of equivalents and the doctrine of prosecution history estoppel is Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co.

Petitioner Festo Corporation owns two patents for an improved magnetic rodless cylinder, a piston-driven device that relies on magnets to move objects in a conveying system. The device has many industrial uses and has been employed in machinery as diverse as sewing equipment and the Thunder Mountain ride at Disney World.

Shoketsu Kinzoku Kogyo Kabushiki Co. entered the market with a device that used one two-way sealing ring and a nonmagnetizable sleeve. Festo Corporation already owned two similar patents (although their initial patent application was rejected) for this industrial device.

Festo filed infringement suite against Shoketsu under the DOC.

Petitioner’s patent applications, as often occurs, were amended during the prosecution proceedings. The application for the first patent (U.S. Patent No. 4,354,125), 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. The inventor submitted a new application designed to meet the examiner’s objections and also added certain references to prior art. The second patent (U.S. Patent No. 3,779,401), was also amended during a reexamination proceeding. The prior art references were added to this amended application as well.

Shoketsu claimed that prosecution history estoppel should bar Festo from asserting equivalents.

Court’s Decision

According to the United States District Court for the District of Massachusetts, Festo’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. 72 F.3d 857 (1995). We granted certiorari, vacated, and remanded in light of our intervening decision in Warner-Jenkinson v. Hilton Davis Chemical Co.After a decision by the original panel on remand, 172 F.3d 1361 (1999), the Court of Appeals ordered rehearing en banc to address questions that had divided its judges since decision in Warner-Jenkinson.

The en banc court reversed, holding that prosecution history estoppel barred Festo from asserting that the accused device infringed its patents under the doctrine of equivalents. 234 F.3d 558 (2000). The court held, with only one judge dissenting, 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. Id., at 566. More controversial in the Court of Appeals was its further holding: When estoppel applies, it stands as a complete bar against any claim of equivalence for the element that was amended. Id., at 574—575. The court acknowledged that its own prior case law did not go so far. Previous decisions had held that prosecution history estoppel constituted a flexible bar, foreclosing some, but not all, claims of equivalence, depending on the purpose of the amendment and the alterations in the text. The court concluded, however, that its precedents applying the flexible-bar rule should be overruled because this case-by-case approach has proved unworkable. In the court’s view a complete-bar rule, under which estoppel bars all claims of equivalence to the narrowed element, would promote certainty in the determination of infringement cases.

Source:

 

http://en.wikipedia.org/wiki/Prosecution_history_estoppel

http://en.wikipedia.org/wiki/Festo_Corp._v._Shoketsu_Kinzoku_Kogyo_Kabushiki_Co.

http://papers.ssrn.com/sol3/papers.cfm?abstract_id=455380

 

Biplab Dey

Knowledge Scientist

Dolcera

 

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