A Subtle Claim Interpretation

Periodically, we are reminded that patent practitioners must be wordsmiths and that the precision of language plays a central role in our patent work. Many patent disputes turn on a single term. The interpretation of a common noun can decide whether or not a patent claim is infringed. Or the construction of an ordinary adjective can render a patent claim invalid. A challenge is that dictionaries do not always provide the meaning of a claimed term. Instead, the specific context of the patent points to the proper interpretation.

The meaning of “periodically” was the issue in a recent case (inter partes reexamination: Hill-Rom vs. Matal, Fed. Cir. Dec. 15, 2017, see Slip Op. pages 7-10) (nonprecedential). The claim required a “control system that periodically verifies the functionality of each module.” Most dictionaries identify two definitions. One meaning, somewhat narrow and proffered by the patentee, would require verifications performed at regular intervals such that the same amount of time elapses between successive verifications. Another interpretation, relatively broader, would not require regular intervals between verifications, but only that they happen from time to time, or occasionally.

In this case, the Court of Appeals rejected the first definition and introduced a third option, by refining the second interpretation (not requiring regular intervals) into two other possible meanings. Thus, the Court identified a broadest possible meaning where the claims would cover verifications that “happen randomly (i.e., on an ad hoc basis)”. The Court further identified a more “reasonable” interpretation under which “periodically” connotes repetition, and “must repeat at spaced time intervals, though, not necessarily at equally spaced time intervals.” I fail to see how random verifications do not also “repeat at spaced time intervals.” But in any event, the Court adopted this interpretation, which excludes random verifications, based heavily on the context of the patent, i.e., its specification, the language of all the claims and the arguments and amendments made during prosecution. Within this intrinsic evidence, the Court focused on statements in the specification that described a control system relying on messages being transmitted at “specified times” and implemented with a timer. The Court also looked to the prosecution history when the claims were distinguished over the prior art teaching “an ad hoc or intermittent self-diagnosis process” not “on any periodic schedule.” Having construed “periodically” in this manner, the Court went on to find the patent not invalid over the prior art, which disclosed random verifications.

Claim interpretation can be tricky. It is entirely dependent on the context of the specific patent at issue. The line between relying on the intrinsic evidence and improperly bringing limitations from the specification into the claims can be fuzzy. In the above decision, for example, the Court seemed to suggest that, based on the specification, “periodically” also required that the modules transmit a status message without prompting from an external source. Such a requirement about who sends the verification messages (modules vs external source) seems to go beyond the temporal nature of the claimed limitation. Thus, a patent practitioner is faced with uncertainty when trying to predict how a judge (at the Patent Office, the ITC, or in federal court) will ultimately interpret a claim. Claim diversity can provide back-up positions in light of this unpredictability, and is often a sign of patent quality. For example, in the above case, a diverse claim set could would have had different claims reciting different expressions, such as “a control system that repeatedly verifies the functionality of each module,” “wherein the control system verifies at regular intervals,” “wherein the control system verifies at specified times,” “wherein the control system verifies based on signals received from the modules,” “based on time schedule,” etc. Diversity in claim language can later prove to be critical even for terms that seem unimportant during prosecution. Creating such diversity requires time, efforts and budgets. But for companies aiming to monetize and/or assert their patents, such an investment of resources should pay off, at least periodically.