Primos, Inc. v. Hunter’s Specialties, Inc.

Primos, Inc. (plaintiff) held a patent for a game-call apparatus used by hunters to simulate animal sounds. The patent’s claims described a device that was designed to be placed entirely inside a person’s mouth and that consisted of a frame, a membrane stretched over the frame, a flexible peripheral edge, and a plate above the frame and over part of the membrane. If a user held the apparatus in place with his tongue and blew, the membrane would vibrate and create an animal sound. The plate, which was the invention’s key improvement upon prior art, provided a constant distance above the membrane and resisted upward pressure from a user’s tongue. During patent prosecution, or the examination process to obtain a patent, Primos was required to make two amendments to the patent claims. First, Primos was required to specify that the plate would have a length, although it was not required to specify what that length would be. Second, it was required to add a limitation stating that the plate would be differentially spaced above the membrane, meaning that there would be varying distances between the parts. Primos sued competitor Hunter’s Specialties, Inc. (Hunter’s) (defendant) for patent infringement. Hunter’s produced a similar game-call apparatus that had a dome above the membrane rather than a plate. The district-court jury held that the Hunter’s product both literally infringed Primos’s patent and infringed it under the doctrine of equivalents. The doctrine-of-equivalents finding was based on the conclusion that the dome produced by Hunter’s was equivalent to Primos’s plate. Hunter’s appealed, arguing that application of the doctrine of equivalents was barred by prosecution-history estoppel and the all-limitations rule.