Proper uses of a means plus function limitation

Posted On :April 9th, 2012 By James Yang

The following case illustrates my propensity for limiting my use of what patent attorneys call the means plus function claim limitation.  There are particular uses for means plus function limitations but more often than not, they seem to be more trouble than they are worth.  I will go over some instances where I think that they are useful down below.

Background of means plus function limitations

A means plus function limitation is a claiming strategy that follows the format of the word MEANS plus a stated FUNCTION.  On its face, it appears very broad.  One would think that a means for fastening would encompass everything known to man that would allow one to fasten two objects.  However, this couldn’t be further from the truth.  In fact, this claim only covers the structure disclosed in the specification and clearly linked to the function stated in the means plus function limitation.  To ensure proper use of a means plus function limitation, one would have to expressly state in the specification that there is a particular function and a particular component of a widget performs such function.  Anything less would leave open the possibility that the claim could be held invalid for being indefinite as was the case for the case discussed below.

Explanation of Ex Parte Adelman

In Ex Parte Adelman, the inventor used the phrase “means for designating a plurality of members as participants in an online business community.”  To perform the analysis, you look for the stated function.  In this case, the stated function is – designating.  You then look to the specification to see what structure, if any, is disclosed in the specification that might perform the designating function.  Thereafter, you must see if such structure is linked to performing the function.  In this case, the inventor pointed to various portions of the specification that allegedly disclosed the structure that performed the function.  The Board of Patent Appeals and Interferences (BPAI) disagreed.  They held that the claim is for a computer enabled means plus function limitation, there must be some form of algorithm corresponding to the function.  The portions of the specification pointed out by the inventors disclosed generic computerized databases, but no algorithm corresponding to the designating function.  Because the specification disclosed no structure to perform the claimed function, the BPAI held that the claim was invalid for being indefinite.

Patent drafting tip

Given the heightened requirement to properly claim an invention as means plus function, the patent application must be drafted with the end in mind.  The claims should be drafted first which many patent attorney do already, then as you draft the patent application, there must be a discussion of a function and the corresponding structure or algorithm that performs the function. This is a bit like working backward but it is necessary for proper drafting of the specification.

Not always broader

The means plus function limitation isn’t always broader even though it might sound very broad on its face.  Let’s take a simple example.  If one claims a means for fastening parts A and B and discloses a nut and bolt in the specification, then this means plus function limitation would cover these things plus their equivalents.  Most likely, it wouldn’t cover an adhesive or magnetic connection or welding because these types of connections are so different.

Now, let’s say that we claim just a “fastener”.  If this is construed normally, then it would potentially include the nut and bolt and probably include the magnetic fastener.  It may even potentially include adhesives and welding.

Making an end run around Festo

Many years back, the seminal Festo case was decided by the United States Supreme Court.  The essence of the case held that if an amendment was made to narrow a claim then such limitation cannot be broadened by the Doctrine of Equivalents.

A basic patent law discussion is necessary at this point.  Infringement can be found if the accused device incorporates all of the limitations of the claim.  If so, this is known as literal infringement.  However, even if the accused device does not incorporate all of the limitations of the claim, infringement can still be found under the Doctrine of Equivalents if the differences are only insubstantial.  Hence, the Festo case held that the infringement analysis does not proceed to the second step or the Doctrine of Equivalents step for the narrowing limitation.  It is not broadened under the Doctrine of Equivalents.

The claim construction for means plus function limitations is a bit different.  No enlargement is given to the claim under the Doctrine of Equivalents.  Rather, the statute which controls how one interprets a means plus function limitation folds equivalents into the literal infringement step.  The statute says that the means plus function shall include the structure disclosed in the specification and equivalents.  Hence, if an amendment to a claim is made, it could conceivably be made in the means plus function format to potentially narrow the limitation but still have some form of equivalents available.

Let’s take our fastener example.  If a claim to a fastener is rejected but you believe that you can obtain allowance for a nut and bolt, then what are the possible ways to claim this to obtain the broadest protection.  If you claim just a nut and bolt, then you are limited to a nut and bolt and exclude other forms of fastening.  If you claim a means for fastening, then you obtain protection for the nut and bolt version plus its equivalents.

Claim strategy when multiple embodiments are disclosed

The breadth of the means plus function limitation is construed as being directed to all of the embodiments disclosed in the specification that are sufficiently linked to the function recited in the means plus function limitation.

If you have multiple embodiments, then it could be significantly less expensive to include one means plus function limitation than to include multiple independent claims in an attempt to cover each of the embodiments.  For example, if you disclose a nut and bolt, welding, adhesives, rivets, etc., you can claim all of these embodiments by using a means for fastening limitation instead of having to recite each one individually. Regardless, the means plus function claim should not be the sole claim but should be layered in with other claims that do not use the means plus function limitation.

I invite you to contact me with your patent questions at (949) 433-0900 or Please feel free to forward this article to your friends. As an Orange County Patent Attorney, I serve Orange County, Irvine, Los Angeles, San Diego and surrounding cities.

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Posted in: Claim drafting, Doctrine of Equivalents, Means plus function

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