Construing the “Function” of a Means-Plus-Function Claim Element

Gregory Baran v. Medical Device Technologies (Fed. Cir. 2010)

Dr. Baran sued MDTech for infringing his patents covering automated biopsy instruments. Soon-to-be Federal Circuit Judge Kathleen O’Malley over-saw the district court case. After construing several disputed claims, Judge O’Malley ordered summary judgment of non-infringement. On appeal, the Federal Circuit affirmed.

Means-Plus-Function: I’ll focus on an interesting question raised regarding Baran’s means-plus-function (MPF) limitation. The limitation reads as follows: a “release means for retaining the guide in the charged position.” 

35 USC 112 p6 provides for MPF claim elements expressed “as a means or step for performing a specified function.”  The statute calls for the limitation to be “construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof.”  Federal Circuit precedent has logically added that the statutory “corresponding structure” are structures that perform the claimed function.

What is the Claimed Function?: Here, the Federal Circuit was asked to construe Baran’s MPF element to identify the claimed function.  MDTech argued that the claimed “release means for retaining” required a structure that exhibited both a releasing function and a retaining function.  Dr. Baran argued that the claimed function was only that of retaining.  On appeal, the Federal Circuit agreed with the lower court that the means-preamble “release” added a functional limitation to the claim element.

[T]he claim language recites both a release function and a retention function. Dr. Baran’s argument regarding the placement of the term “release” is unavailing. The relevant inquiry is whether the term at issue is purely functional. See Signtech USA, Ltd. v. Vutek, Inc., 174 F.3d 1352, 1356 (Fed. Cir. 1999) (construing “ink delivery means” to be equivalent to “means for ink delivery” because “ink delivery” was purely functional language); Al-Site Corp. v. VSI Int’l, Inc., 174 F.3d 1308, 1318 (Fed. Cir. 1999) (“[W]hen it is apparent that the element invokes purely functional terms . . . the claim element may be a means-plus-function element despite the lack of express means-plus-function language.”). In the context of the ’797 patent, the term “release” is not an idle description but a vital function to be performed by the means-plus-function element. The patent does not recite a biopsy instrument that retains indefinitely without release; rather, the contemplated function is to retain for the express purpose of producing a spring-loaded release on demand. The claim language ties both functions to the same means-plus-function element, so it is appropriate that the element be construed accordingly.

Although it is difficult to take-away lessons from claim construction decisions, a potential best-practices approach to drafting MPF claims may be to eliminate any adjectives tied directly to the “means.”  Of course, my best practice suggestion is intended for those times when you want to draft MPF claims with clarity.

Federal Circuit Splits on Validity of Means Plus Function Claim

Telcordia Technologies, Inc. v. Cisco Systems pic-100.jpg (Fed. Cir. 2010)

Chief Judge Rader and Judge Prost sparred over the level of explanation necessary to ensure that a means plus function (MPF) claim is found definite. The Patent Act (35 U.S.C. 112 p6) permits claim limitations written as a "means or step for performing a specified function." The statute provides that an MPF "claim [limitation] shall be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof." However, the claim will be found indefinite and therefore invalid if the specification fails to include at least some structure that is clearly linked or associated with the claimed function. “The question is not whether one of skill in the art would be capable of implementing a structure to perform the function, but whether that person would understand the written description itself to disclose such a structure.” (Quoting Tech. Licensing Corp. v. Videotek, Inc., 545 F.3d 1316, 1338 (Fed. Cir. 2008)).

Telcordia's patent in this case is directed to a double-ring network that is designed to withstand either a line-cut or a failed node. One element of the claim requires a "monitoring means, associated with the first ring and the second ring, for evaluating the integrity of the multiplexed subrate communications on the first ring and the second ring."

Writing for the majority, Chief Judge Rader (joined by Judge Lourie) held that the claimed "monitoring means" had been properly described in the specification. The dissent cited the same precedent but could not find anything in the specification that links disclosed structures to the claimed function. In discussing the opinion, Foley's Hal Wegner described the opinion as "pitting the leader of the older generation [of Federal Circuit Judges] against a contender from the next generation."

Stats: About 15% of newly issued patent included at least one claim having an MPF limitation. And, of those patents that include an MPF limitation, about half recite fewer than five such limitations. It appears that attorneys are using MPF claim language primarily as a back-up. Longer claim-sets are more likely to include means-plus function language. Thus 21% of patents with above-average-sized claimsets (by character count) include a means-plus-function limitation while only 11% of patents with below-average-sized claimsets include an MPF limitation. Looking claim-by-claim, I found that only 3% of the recently issued patents include means-plus-function limitations in every independent claim. Patents with MPF terms are more frequently associated with non-assigned patents (usually individual inventors). Patents arising from certain countries are much more likely to include MPF limitations. The chart below looks at the most common foreign filing jurisdiction for priority claims and reports the percentage of US patents arising from those foreign filings that include MPF limitations. [More Data]


Blackboard: Federal Circuit Again Find Software-Related Means-Plus-Function Claims Invalid for Failing to Disclose Sufficient Structure

Blackboard v. Desire2Learn (Fed. Cir. 2009) 08-1368.pdf

Blackboard’s patent covers an internet-based educational support system and method. (U.S. Pat. No. 6,988,138). On summary judgment, the district court (Judge Clark, E.D. Tex.) found claims 1-35 invalid as indefinite, but a jury found found that Desire2Learn liable for infringement of claims 36-38. On appeal, the Federal Circuit agreed that Claims 1-35 are indefinite, and – after altering the claim construction – held that the remaining claims were also invalid as anticipated. pic-54.jpg

Means-Plus-Function: Blackboard’s seemingly broadest claim (claim 1) includes several means-plus-function clauses, including a “means for assigning a level of access and control.” The specification briefly discusses an “access control manager” (ACM) with an “access control list.” On appeal, however, the court found that brief description to be an insufficient “disclosure of the structure that corresponds to the claimed function” and consequently indefinite under 35 U.S.C. §112 ¶2. See In re Donaldson, 16 F.3d 1189 (Fed. Cir. 1994)(en banc).

“[W]hat the patent calls the ‘access control manager’ is simply an abstraction that describes the function of controlling access to course materials, which is performed by some undefined component of the system. The ACM is essentially a black box that performs a recited function. But how it does so is left undisclosed.”

Important for patent drafter, means-plus-function claims require disclosure in the specification even if the means are already well known in the art.

The fact that an ordinarily skilled artisan might be able to design a program to create an access control list based on the system users’ predetermined roles goes to enablement. The question before us is whether the specification contains a sufficiently precise description of the “corresponding structure” to satisfy section 112, paragraph 6, not whether a person of skill in the art could devise some means to carry out the recited function.

Because claims 2-35 all depend upon claim 1, they are all invalid as indefinite

Claim construction: At the trial, Blackboard’s expert could only identify one difference between claims 36-38 and the prior art. Namely, that the Blackboard patent identified a “single login” feature that allowed one user to have various roles within the system. “For example, Blackboard asserted that its claimed method would allow a graduate student who was a student in one course and a teacher in another to use a single login to obtain access to both courses and to obtain access to the materials for each course according to the graduate student’s role in each.” However, on appeal, the Federal Circuit determined that the claims do not actually require that feature — leading them to hold the claims invalid based primarily on the admissions of Blackboard’s own expert.

[O]nce the claims are properly construed, the conclusion of anticipation is dictated by the testimony of Blackboard’s own witnesses and the documentary evidence that was presented to the jury. Based on that evidence, and in the absence of a “single login” requirement in claims 36-38, it is clear that the prior art contains every limitation of those claims.

Defendant Desire2Learn wins a complete victory (after a few million in attorney fees).

Anticipation Requires More Than Disclosing All the Elements

Net MoneyIn v. Verisign (Fed. Cir. 2008)

NMI sued Verisign and others for infringing its credit card processing patent. One of NMI’s claims was found anticipated by a single prior art reference. That reference taught each element in the invalidated claim. However, there was no single example that taught all the elements together.

On appeal, the Federal Circuit reversed – holding that anticipation takes more than simply locating each element within the four corners of a single document.

In its rebuttal, the appellate panel focused on the concept anticipating the invention. To anticipate, the prior art must teach all the claim elements and the claimed arrangement.

Section 102 embodies the concept of novelty—if a device or process has been previously invented (and disclosed to the public), then it is not new, and therefore the claimed invention is “anticipated” by the prior invention. . . . Because the hallmark of anticipation is prior invention, the prior art reference—in order to anticipate under 35 U.S.C. § 102—must not only disclose all elements of the claim within the four corners of the document, but must also disclose those elements “arranged as in the claim.”

Focusing for a moment on arrangement – to anticipate, the reference must teach “all of the limitations arranged or combined in the same way as recited in the claim.”

Applying the rule to this case, the appellate panel found that the prior art reference was not anticipating. The reference disclosed two transaction protocols, but neither protocol contained all of the elements combined in the manner claimed. “Thus, although the iKP reference might anticipate a claim directed to either of the two protocols disclosed, it cannot anticipate the system of claim 23. The district court was wrong to conclude otherwise.”

Means Plus Function: After claim construction, the district court also found NMI’s means-plus-function claims invalid because they lacked any corresponding structure in the specification. On appeal, the Federal Circuit affirmed.

The patent statute allows patentees to draft claims in more generic ‘means plus function’ language. That language allows a patentee claim various elements based on their function. However, means plus function claims are only valid if the specification describes some structure to carry out the proposed function. According to the courts, this structure requirement is separate from any enablement requirement. Thus, some structure must be provided in the specification even if one skilled in the art would not need that disclosure to make the invention.

Here, NMI claimed a “[a bank computer including] means for generating an authorization indicia” but did not provide any corresponding structure in the specification to perform that structure.

On appeal, NMI incredibly argued that the claim was not a means-plus-function claim. The Federal Circuit disagreed – finding that the claim lacks structure.

Searching for structure in the specification, NMI pointed to its recitation of a “bank computer.” Of course that recitation is insufficient.

‘To avoid purely functional claiming in cases involving computer-implemented inventions, we have “consistently required that the structure disclosed in the specification be more than simply a general purpose computer or microprocessor.” Quoting Aristocrat

Consequently, a means-plus-function claim element for which the only disclosed structure is a general purpose computer is invalid if the specification fails to disclose an algorithm for performing the claimed function.

Holding of MPF claim invalidity affirmed.

Finisar v. DirecTV: Software Means-Plus-Function Claim must be Supported by Particular Structure

Finisar v. DirecTV (Fed. Cir. 2008) [This is Part II of the case discussion. Read Part I]

In a cross-appeal, Finisar asked the CAFC to overturn the lower court’s findings that its means-plus-function claims were invalid for failing to disclose any particular structure to perform the claimed function.  A patent applicant is allowed to claim that her invention covers the “means” for accomplish certain results so long as the application also discloses the “structure” for accomplishing the result.  That structural disclosure must be found somewhere in the specification. Means plus function claims are generally easier to write and are thought by many to be quite broad. Over the past decade, however, courts have increasingly been wary of particularly overbroad claims.

In this case, the claimed means and functions were software related. A number of CAFC cases have required that software means-plus-function claims provide more structural disclosure than just a general purpose computer. Rather, the disclosure must be “the special purpose computer programmed to perform the disclosed algorithm.” WMS Gaming; See also Aristocrat. The CAFC sees its structure requirement as quite minimal and easy to satisfy. Here, however, the complete lack of structure leaves the claims so vague that “one of skill simply cannot perceive the bounds of the invention.”


  • One of the Finisar MPF clauses reads as follows:
    • database editing means, coupled to said one or more computer memory devices, for generating a hierarchically arranged set of indices for referencing data in said information database, including distinct indices for referencing distinct portions thereof, and for embedding said indices in said information database . . .”

Computer Implemented Means-Plus-Function Element Must be Supported by Specific Algorithm in Specification

ScreenShot014Aristocrat Technologies Australia (ATA) v. International Gaming Technology (IGT) (2007-1419) (Fed. Cir. 2008)

ATA and IGT have two parallel cases pending before the CAFC. This appeal focuses on whether ATA’s asserted claims are invalid as indefinite. (U.S. Pat. No. 6,093,102). The other pending case questions whether the PTO properly revived ATA’s unintentionally abandoned national stage application. (U.S. Pat. Nos. 7,056,215 and 7,108,603) [See Patently-O discussion of revival case].

This case focuses on a patent covering an electronic slot machine patent that allows players to pre-select which combination of symbol locations will be used to determine a winner.

Claims Indefinite: The district court held the claims invalid as indefinite under 35 U.S.C. § 112 ¶ 2. Its opinion focused on the claimed means-plus-function element “game control means” — finding the term indefinite because the specification did not provide “structure” to perform the claimed functions.  The specification did include the statement that the control means could be a microprocessor-based gaming machine with “appropriate programming.” However, the lower court focused on the absence of any “specific algorithm” or “step-by-step process for performing the claimed functions.”

On appeal, the CAFC affirmed, holding that computer implemented means-plus-function claims must include “more than simply a general purpose computer or microprocessor.”  The purpose of the requirement, according to Judge Bryson’s opinion, is to avoid overbroad “pure functional” claims.  Because of the ubiquity of general purpose computers, a bare microprocessor cannot be considered a sufficiently specific structural disclosure:

For a patentee to claim a means for performing a particular function and then to disclose only a general purpose computer as the structure designed to perform that function amounts to pure functional claiming.

Within PHOSITA’s Ability: The algorithm missing from ATA’s disclosure is almost certainly within the ability of an ordinary game programmer.  In fact, I believe that it would only take me (a law professor) only a few hours to create a rough algorithm showing how the ATA software program could operate.  Judge Bryson shot-down that argument: Structure for a means-plus-function element must be provided in the specification regardless of whether the structure is already well known in the art.

What is Required: “Source code” is not required to be disclosed, nor is a “highly detailed description of the algorithm.”  However, a computer oriented application using means-plus-function claims must “at least disclose the algorithm that transforms the general purpose microprocessor to a “special purpose computer programmed to perform the disclosed algorithm.” (Quoting WMS Gaming)


CAFC: “Circuit means” interpreted as means-plus-function

PatentlyO2006029DESA IP v. EML Tech and Costco (Fed. Cir. 2007 – NONPRECEDENTIAL).

DESA owns a patent directed to motion-activated security lights. The lights have a low-level always-on illumination as well as a bright security illumination that is activated when motion is detected by a passive infrared motion sensor. During infringement litigation, the district court construed the claims and consequently entered a stipulated judgment of noninfringement.

The appeal focused on whether the disputed claim phrases — “sensor means,” “control circuit means,” and “switching means” — should be interpreted as means-plus-function.

The use of the word “means” in the claim language invokes a rebuttable presumption that § 112, ¶ 6 applies; conversely, the failure to use “means” invokes a presumption that § 112, ¶ 6 does not apply. . . . Nonetheless, the presumption that § 112, ¶ 6 applies may be rebutted if the claim recites no function or recites sufficient structure for performing that function.

Distinguishing earlier precedent, the CAFC determined that neither the sensor, control circuit, nor switching pre-means terms recited sufficient structure.

DESA argues that this court has previously stated that “it is clear that the term ‘circuit’ by itself connotes some structure.” In Apex, however, the word “means” was not used, so the reverse presumption—i.e., that § 112, ¶ 6 does not apply—was invoked.

Regarding interpretation of the claims, the CAFC found that the district court had improperly given the terms a narrow construction by focusing on the preferred embodiments and the figures.