The word “only” is one of those magic words in patent specifications and claims. The word conveys such a strong absolute that it tends to drown out other arguments. And, given the law of unintended consequences, patent drafters should have a very good reason to use this word in their applications.
A recent case, Markem-Imaje Corp. v. Zipher LTD., 657 F.3d 1293 (Fed. Cir. 2011), underscores this point and illustrates how even the most innocuous use of the term “only” can be a troublesome fact in litigation. The patent in the case addresses how motors position printer ribbon in industrial thermal printers. The ribbon is held on two spools, being taken from one spool and collected on the other. The patent characterized the general approach taken by prior art printers, stating that they “drive only the spool onto which ribbon is taken up” (7,150,572, 1:37-38). The use of the term “only” here, especially because it was being used to characterize the prior art, seems harmless enough at first.
Enter patent litigation. The accused infringer formulated a non-infringement position and argued that “drive” had to mean “rotate” and not merely the application of a torque, which includes where the motor is active but stationary. The district court agreed, and, a key fact in the district court’s interpretation of the claim term was the patent’s use of the term “only.” The district court reasoned that “drive” cannot mean “apply torque” or else the specification would not have stated that only the spool onto which ribbon is taken up is driven in the prior art devices. The other spool in the prior art devices had torque applied. The court went with the narrower meaning of the term “drive,” and in turn, found no literal infringement on summary judgment.
Although the use of “only” in the specification wasn’t the only fact in the court’s analysis and ultimately the court’s construction was overturned on appeal, the use of the term “only” was a fact completely within the patent drafter’s control. For patent professionals reviewing draft applications, the term “only” should at the very least raise a red flag and warrant additional scrutiny. Often, the sentence can be rephrased without using the term, and the potential for problems down the road can be reduced.
A copy of the opinion from the Court of Appeals for the Federal Circuit in Markem-Imaje Corp. v. Zipher LTD may be found here.