Festo Corp. v. SMC Corp. (Fed. Cir. 2007).
In 1988, Festo sued SMC for infringement of its magnetized pistons. Since then, the CAFC has issued numerous Festo opinions including two en banc. The Supreme Court has also ruled twice. This appeal, like many of the others involve the scope and limits of the doctrine of equivalents (DOE).
Doctrine of Equivalents: While patent claim language traditionally defines the patent right, the doctrine of equivalents occasionally allows for a finding of infringement even when an accused product falls outside the literal limits of claim language. More particularly, DOE applies when a claim limitation differs insubstantially from the accused product or if the accused element performs the substantially same function in substantially the same way with substantially the same result (function/way/result test).
Prosecution History Estoppel: A narrowing claim amendment made during prosecution creates a presumption that the element should be narrowly interpreted — legally precluding application of the DOE. In its 2002 Festo decision, the Supreme Court noted three exceptions that would allow for DOE infringement even after a narrowing amendment: (1) the equivalent was unforeseeable; (2) the reason for the narrowing amendment was only tangentially related to the equivalent; or (3) “some other reason…”.
Foreseeable Equivalent: In this case, Festo’s amendment was narrowing, but the patentee argued that SMC’s equivalent was unforeseeable to one of ordinary skill at the time of the amendment. The question was whether the accused product’s aluminum sleeve was a foreseeable alternative of the claimed magnetizable sleeve. Aluminum sleeves were already well known in the art, but Festo argued unforeseeability because no PHOSITA knew that the aluminum sleeve would serve as a magnetic shield (the function of the sleeve). This unknown function — according to Festo — made the use of aluminum unforeseeable. In its briefs, Festo attempted to find a requirement for functional foreseeability in the function/way/result test of DOE.
The CAFC rejected Festo’s argument and instead found that foreseeability should be broadly interpreted — finding “that an alternative is foreseeable if it is disclosed in the pertinent prior art in the field of the invention. In other words, an alternative is foreseeable if it is known in the field of the invention as reflected in the claim scope before amendment.” This result follows the court’s 2003 en banc decision that later developed and nonanalogous technology are “usually not foreseeable” — but that equivalents already known in the relevant field are generally foreseeable.
Here, the CAFC went a step further — implying that the question of whether a PHOSITA could have known the suitability of a particular a alternative is not relevant 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.”
Consequently, the aluminum sleeve was seen as foreseeable – and thus prosecution history estoppel applies to block the doctrine of equivalents.
Dissent: Judge Newman dissents – noting that the opinion is “confound[ing]”, “incorrect”, and “futher erodes the residue of the doctrine of equivalents.”