US Court Rules that Foreseeability Creates No Bar to Use of Doctrine of Equivalents

On 19 February 2014, the U.S. Court of Appeals for the Federal Circuit (CAFC) made a second-instance ruling on Ring & Pinion Service Inc. v. ARB Corporation Ltd. The central issue of the case was whether the doctrine of equivalents was still applicable if an equivalent was foreseeable at the time of filing a patent application. The unanimous decision of CAFC held that foreseeability did not preclude the use of the doctrine of equivalents, overturning the holding of the district court that granted summary judgment of non-infringement.
The allegedly infringing product only differed from the technical solution of the patent in dispute in its use of "cylinder" in claim construction, as contrasted to "cylinder means formed in …" of the patent in suit. In fact, both the plaintiff and the defendant agreed that "cylinder" was an equivalent feature, and acknowledged that the equivalent was foreseeable by those skilled in the art at the time of filing the patent application.
Regarding the focal point of dispute, CAFC pointed out that there had never been a foreseeability limitation on the application of the doctrine of equivalents, while in light of previous case law, it was clear that "known interchangeability" supported a finding of infringement under the doctrine of equivalents. Hence, precluding a finding of equivalence infringement of a technical feature foreseeable by those skilled in the art at the time of filing the patent application would be contradictory to the judicial precedents.
Following the reasoning of the case, it may be worthwhile to note that whether to include an equivalent in the description can mean different outcomes in findings of equivalence infringement. For a foreseeable equivalent, exclusion of it from the description makes the claim for equivalent infringement allowable; whereas under the effect of the rule of dedication, inclusion of the equivalent may bar the claim for equivalent infringement.