I think the big picture lesson here is twofold: (1) avoid saying more than is necessary to distinguish over the art, and (2) try to limit your characterizations to the art itself rather than the claimed invention. The patentee in this case did just that and no prosecution history estoppel was found to attach.
Background / Facts: The patent at issue was directed to a “platform” that stabilizes a camera for filming motion pictures from moving vehicles, for which the inventor David Grober won an academy award. The district court relied heavily on the reexamination history of the patent in determining that Grober had narrowed the claims “in order to avoid a significant body of prior art.” During reexamination, Grober distinguished his invention by explaining that the prior art does not teach “the second sensor package being fixed to the payload platform.” He asserted that the prior art “never uses the word ‘fixed to’ or ‘mounted on’ to describe [its] potentiometers [sensors] 27 and 29. They are clearly not ‘fixed to,’ and most definitely not ‘wholly fixed to’ Platform Structure 18.”
Issue(s): Whether these prosecution history statements warrant a narrower interpretation of the claimed “payload platform” as being limited to a horizontal surface.
Holding(s): No. Prosecution history estoppel only applies to a “clear and unmistakable disavowal of scope during prosecution.” These statements do not unambiguously focus on the characteristics of the “payload platform” itself, let alone distinguish it from the prior art as being a two-dimensional surface. Instead, they merely refer to the placement of the prior art sensors in relation to the element identified by the examiner as the “payload platform,” but do not address the characteristics of the claimed “payload platform” itself. Thus, these ambiguous statements do not disavow or even clearly describe the structure of the claimed “payload platform.”