Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co.,

"When Amendments Speak Louder Than Words — The Reach of the Doctrine of Equivalents”

Short Description:

This is a U.S. Supreme Court case addressing how amendments made during the patent prosecution process affect the ability of a patent holder to later claim infringement under the Doctrine of Equivalents. The question is whether narrowing amendments always bar equivalents for the amended portions, or only in certain circumstances.

Facts:

• Festo Corporation owned two patents for a magnetic rodless cylinder device.

• During patent examination, Festo amended the claims: in one patent they added limitations including that the device would contain two one‐way sealing rings and that the outer sleeve be magnetizable.

• The second patent was also amended (in reexamination) to include the sealing rings limitation.

• A competitor (Shoketsu Kinzoku Kogyo Kabushiki Co., “SMC”) began selling a device that was similar but differed in key respects: it used a single two‐way sealing ring rather than two one‐way sealing rings, and a non‐magnetizable sleeve rather than a magnetizable one.

• Festo sued alleging infringement under the Doctrine of Equivalents. SMC responded that Festo’s amendments during prosecution should estop (prevent) Festo from claiming equivalents for what was surrendered in those amendments.

Issues / Questions:

1.     Does prosecution history estoppel apply only when amendments are made to avoid prior art, or more broadly whenever claim amendments narrow a claim to satisfy any requirement of the Patent Act?

2.     If estoppel applies, is it an absolute bar against any equivalents for the amended element, or is there room for some equivalents under certain conditions?

Suggestion / Arguments (from the parties):

• Festo argued that the amendments were made to satisfy requirements under § 112 of the Patent Act (description, clarity etc.), not merely to avoid prior art. They asserted that not all narrowing amendments should automatically bar claim to equivalents.

• SMC argued that any narrowing amendment made for a reason related to patentability (including formal or descriptive defects) should trigger prosecution history estoppel, and that once estoppel applies for an amended element, that element cannot be the basis for an equivalents claim.

Findings / Judgment:

• The Supreme Court held (unanimously) on May 28, 2002 that while prosecution history estoppel may apply to any claim amendment made to satisfy a requirement of the Patent Act (not only amendments to avoid prior art), such amendments do not automatically create a complete bar against all equivalents for the amended element.

• Instead, the Court established a rebuttable presumption: when a claim is narrowed by amendment for a reason relating to patentability, the patentee is presumed to have surrendered all equivalents for that amended element. However, the patentee may overcome the presumption if they can show one of several exceptions, including that the particular equivalent was unforeseeable at the time of amendment, that the rationale for the amendment is only tangentially related to the equivalent in question, or that there was some other reason the patentee could not reasonably have described the alleged equivalent earlier.

• The Court remanded the case back to lower courts to apply this test (i.e. to determine what territory was surrendered, whether the presumption is rebutted with respect to the particular equivalents asserted by Festo).

Judgement Date:

May 28, 2002