Festo diagThe Federal Circuit Court of Appeals, in Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd., No. 05-1492, drove another nail in the coffin of the doctrine of equivalents. This case — pending for almost twenty years and before the Supreme Court twice and twice at the CAFC en banc — looks at the scope of prosecution history estoppel under the doctrine of equivalents.

In a patent dispute involving a magnetically coupled piston, the Federal Circuit upheld a judgment of non-infringement after answering the question of whether an equivalent is foreseeable within the meaning of Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722, 740 (2001) (Festo VIII), and subject to surrender under the doctrine of prosecution history estoppel.

The Supreme Court, in vacating and remanding an earlier decision, held that an amendment did not raise a complete bar, and that there were three exceptions that (1) the equivalent was unforeseeable at the time of the application, (2) the rationale underlying the amendment [bears] no more than a tangential relation to the equivalent in question, or (3) that some other reason suggest[s] that the patentee could not reasonably be expected to have described the insubstantial substitute in question.

In Graver Tank, the Supreme Court stated that the doctrine of equivalents applies when the equivalent represents an insubstantial change from the claim language. The Court also explained that a patentee may invoke [the] doctrine [of equivalents] to proceed against the producer of a device if it performs substantially the same function in substantially the same way to obtain the same result. The doctrine of prosecution history estoppel acts as a legal limitation on the doctrine of equivalents.

“[P]rosecution history estoppel limits the range of equivalents available to a patentee by preventing recapture of subject matter surrendered during prosecution of the patent.” The burden is on the patentee to establish that the reason for the amendment was unrelated to patentability. If the patentee fails to meet this burden, the court must presume that the patentee “had a substantial reason related to patentability for including the limiting element added by amendment.” If there is a substantial reason related to patentability “prosecution history estoppel would bar the application of the doctrine of equivalents as to that element.”

This case raises the question of whether an equivalent is foreseeable within the meaning of Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722, 740 (2001) (“Festo VIII”), and subject to surrender under the doctrine of prosecution history estoppel. The Federal Circuit has now held that foreseeability does not require the applicant to be aware that a particular equivalent would satisfy the insubstantial differences test or the function/way/result test with respect to the claim as amended.

The court stated that an equivalent is foreseeable when the equivalent is known in the pertinent prior art at the time of amendment. For example, in Amgen Inc. v. Hoechst Marion Roussel, Inc., 457 F.3d 1293, 1313 (Fed. Cir. 2006), the court found that the patentee failed to establish a lack of foreseeability where “the patentee admittedly knew about the . . . equivalent at the time of the . . . amendment” and informed the examiner of the equivalent during prosecution.

The court held that:

[B]oth the Supreme Court’s decision and our en banc decision make clear that an equivalent is foreseeable if the equivalent was generally known to those skilled in the art at the time of amendment as available in the field of the invention as defined by the pre-amendment claim scope. The applicant is charged with surrender of foreseeable equivalents known before the amendment, not equivalents known after the amendment. Thus, for example, the Supreme Court in Festo VIII noted that “[t]he patentee, as the author of the claim language, may be expected to draft claims encompassing readily known equivalents.”

Second, accepting Festo’s view of foreseeability would likely eliminate prosecution history estoppel as a restriction on the doctrine of equivalents in most cases. See Warner-Jenkinson, 520 U.S. at 30. Prosecution history estoppel would apply only if the applicant in adopting the narrowing amendment was aware or should have been aware that the equivalent would be an equivalent to the claimed feature for purposes of the invention as defined by the amended claim. This in itself would be rare, and it would be rarer still that the applicant, aware of such an alternative, would have failed to claim it in the first instance. An alternative would be foreseeable only in the limited circumstances where the alternative was inadvertently omitted and was a candidate for a reissue patent. See 35 U.S.C. § 251.

Third, since the only difference between the function/way/result test for infringement and Festo’s test for prosecution history estoppel is the difference in timing—the function/way/result test for infringement being applied at the time of infringement and the function/way/result test for prosecution history estoppel being applied at the time of amendment—Festo’s proposed test would lead to endless bickering over whether the equivalent satisfied the function/way/result test. It would also lead to inconsistent arguments, as the record in this case amply attests.

Finally, and most important, Festo’s test focuses on the wrong claim. The question is not whether after the narrowing amendment the alternative was a known equivalent, but rather whether it was a known equivalent before the narrowing amendment. The purpose of an amendment typically is to avoid the prior art. If at the time of the amendment, the equivalent was known in the pertinent prior art, the applicant should not be able to recapture it simply by establishing that a property of the equivalent—irrelevant to the broader claim before amendment—was relevant but unknown with respect to the objectives of the narrower amended claim. In other words, an equivalent that is foreseeable as an alternative to the broader claimed feature does not become unforeseeable simply because the claimed feature is narrowed.

Thus, the court concluded that the function/way/result test or insubstantial differences test is inapplicable to the question of foreseeability. An equivalent is foreseeable if one skilled in the art would have known that the alternative existed in the field of art as defined by the original claim scope, even if the suitability of the alternative for the particular purposes defined by the amended claim scope were unknown.

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