United States: Disclosed Embodiment Does Not Necessarily Limit Scope of Means-Plus-Function Limitation

The U.S. Court of Appeals for the Federal Circuit has held that a means-plus-function claim limitation need not necessarily be construed to include all the attributes of the corresponding structure recited in the specification. Instead, a court should look to only so much of the structure as is needed to perform the claimed function. Golight, Inc. v. Wal-Mart Stores, Inc., Case No. 02-1608 (Fed. Cir. Jan. 20, 2004).

Golight sued Wal-Mart for infringing its patent on a wireless, remote-controlled, portable search light. One limitation of the claim at issue required a "horizontal drive means for rotating said lamp unit in a horizontal direction." The only structure in the specification corresponding to a "horizontal drive means" was in the description of the preferred embodiment, which the specification explicitly stated must be capable of rotating through 360°. At trial, Wal-Mart argued its product did not infringe because it was incapable of moving through a full 360°. The trial court disagreed.

On appeal, Wal-Mart argued the district court erred in construing the "horizontal drive means" limitation more broadly than the corresponding structure in the patent specification. Because the patent described only a device that rotated through at least 360°, Wal-Mart argued, the corresponding limitation should have been construed to exclude devices (like the accused device) incapable of 360° rotation. The Court dismissed this argument, pointing out that the specification merely described the preferred embodiment, and patentees are not required to include all of the advantages or features described as significant or important in the written description in each of their claims. With means-plus-function claims, as with more conventional claims, it is improper to import limitations from the specification into the claim. Rather, only so much of the disclosed structure as is necessary to perform the claimed function should be deemed part of the limitation.

Wal-Mart also argued the patentee had acted as its own lexicographer during prosecution when it gave the term "rotating" a special definition, requiring rotation through at least 360°. The Court held, however, the prosecution history cited by Wal-Mart was subject to multiple reasonable interpretations and, therefore, did not constitute a clear and unmistakable departure from the ordinary meaning of the term "rotating."

Practice Note: In construing means-plus-function claims, there is an obvious tension between the rule that the scope of the claim is limited to the corresponding disclosed structure (and equivalents) and the rule that it is improper to import limitations from the specification into the claims. Golight seems to resolve this tension in favor of broad patent scope. Absent a clear indication of a different intent on the part of the patentee, it appears the Federal Circuit will be willing to grant means-plus-function claims the broadest possible scope supported by the written description and consider additional details in the description to be non-limiting "bells and whistles."