When drafting patent claims for a device, it is often desirable to describe the device based on how it works instead of how it is structured. Describing a device based on how it works is often referred to as "functional claiming." Claims that make use of functional claiming are frequently broader in scope than those that describe a specific device structure.
The U.S. Patent Statute allows applicants to use what is known as "means-plus-function" claiming. In this claim structure, the claim recites a component as a "means for" doing some specified function (e.g., "means for displaying an image"). While this type of claim language appears to be quite broad, it is not. The Patent Statute mandates that claim elements written in "means-plus-function" form be construed as limited in scope to the specific structures disclosed in the specification, and equivalents thereof, which perform the claimed function.
As a result, when using true functional claiming, patent lawyers avoid the use of means-plus-function claiming because the Patent Statute limits terms using this form structurally. One technique is to convert the function into a noun, which gives the claim element the appearance of being structural while remaining essentially functional. Many existing items are already described this way. For example, the term "lock" is a structural analog to a "means for locking." However, patent attorneys will often try to convert other verbs into nouns that are not commonly used in an effort to describe an element functionally. In a less subtle variation of means-plus-function claiming, patent attorneys will also use generic structural nouns or "nonce" words, such as "element," "device," "module," etc. in place of the word "means".
The Federal Circuit has applied a "strong presumption" that a claim element is not to be construed as a "means-plus-function" claim element when the word "means" is not used. Inventio AG v. ThyssenKrupp Elevator Americas Corp., 649 F.3d 1350, 1358 (Fed. Cir. 2011). The Court has also held that this strong presumption is "not readily overcome" and that claim elements which do not include the word "means" will not be subject to means-plus-function treatment unless the limitation is "devoid of anything that can be construed as structure." Flo Healthcare Solutions, LLC v. Kappos, 697 F.3d 1367, 1374 (Fed. Cir. 2012).
In Williamson v. Citrix Online, LLC, No. 2013-1130, slip op. (Fed. Circ. June 16, 2015), the en banc Federal Circuit considered a portion of an earlier opinion and overruled its prior precedents concerning whether and under what circumstances a claim element would be subjected to the claim construction rules applicable to means-plus-function claim elements. A copy of the opinion can be found here. Claim elements that do not use word "means" are still presumed not to be subject to means-plus-function claim construction treatment. However, the presumption is no longer "strong." Slip Op. at 15-16. In addition, the Court overruled the requirement of a showing that a limitation is "essentially devoid of anything that can be considered as structure." Id. at 16. The Williamson Court held that when a claim term lacks the word "means," the presumption that it is not subject to means-plus-function claim construction treatment can be overcome if the challenger demonstrates that the claim term fails to recite sufficiently definite structure or else recites function without reciting sufficient structure for performing that function. However, this presumption is now apparently weaker.
The Williamson decision could have significant impact on patent applicants and patent owners seeking to enforce their patents. When claim terms are treated as means-plus-function terms, the specification must disclose some structure that corresponds to the claimed function. Otherwise, the claim is invalid for indefiniteness. This is exactly what happened in Williamson. Certain of the asserted claims recited the phrase "a distributed learning control module for" performing three specific functions. However, the Court found that the specification failed to associate any structure with one of the recited functions. As a result, because the phrase was subject to means-plus-function treatment, claims reciting that phrase were held invalid for indefiniteness. Slip op. at 25.
In addition, in light of Williamson, claim elements which heretofore would have been interpreted broadly and functionally, may be interpreted narrowly and structurally because they will now be subject to means-plus-function treatment. Such limiting constructions may allow competitors to more easily design around patents.
Because the Williamson Court did not do away with the presumption that claim elements lacking the word "means" are not subject to means-plus-function treatment, it remains to be seen whether and to what extent claim terms that would have avoided means-plus-function treatment in the past will now be subject to such treatment once the district courts start applying Williamson.
suggests that it may be more difficult to effectively claim an invention as an apparatus or device using functional claiming because of the increased likelihood that functionally described claim elements may be treated as means-plus-function elements. Thus, including method claims in patents may be more important than ever. Method claims often allow you to describe an invention in terms of how it operates without using nouns that could be potentially subject to means-plus-function treatment. The drawback is that the direct infringers of method claims are typically customers instead of competitive device suppliers, which means that the suppliers can only be held liable for indirect infringement (i.e., contributory infringement or inducement of infringement). However, that is preferable to having a claim invalidated or found not infringed altogether because a court holds a functionally recited claim element to be subject to means-plus-function treatment.