On Friday, the Federal Circuit issued another in a long line of cases cautioning against the use of means-plus-function language in patent claims.
As previously noted, 35 U.S.C. § 112, sixth paragraph, permits a patent applicant to write a limitation of a patent claim as a means for performing a specific function recited in the claim. In this way, it is not necessary to actually include the specific structure for performing that function in the claim.
The Federal Circuit has interpreted such claim limitations as being limited to those structures and their equivalents that are specifically linked to the function recited in the claim. The specification has to provide the link to make it clear what structures from the specification would meet the claim limitation. If no structure is specifically linked, the claim is invalid as indefinite.
How does one determine if the structure is equivalent to a structure recited in the specification? The Federal Circuit takes a narrow view of this issue as well.
A structure in the accused device constitutes an equivalent to the corresponding structure in the patent only if the accused structure performs the identical function “in substantially the same way, with substantially the same result.”
The function must be identical to that in the claim and the structure must perform the function “in substially the same way, with substantially the same result.”
In Friday’s opinion, the Federal Circuit was to determine whether the claim limitation “latching means” was infringed by the defendant. The “latching means” was recited in clause f) of claim 1 of U.S. Patent No. 5,594,398.
1. A ground fault interrupter (gfi) wiring device for connection in an electrical circuit, said device comprising:
a) housing means defining an enclosed space;
b) at least one pair of electrical terminals fixedly supported in spaced relation within said enclosed space;
c) a unitary, electrically conducting mem-ber carrying a pair of spaced electrical contacts;
d) mounting means for said conducting member to permit movement thereof be-tween a first position, wherein said pair of contacts are in respective, circuit-making engagement with said pair of terminals, and a second position, wherein both of said pair of contacts are in spaced, circuit-breaking relation to said pair of terminals;
e) biasing means urging said conducting member toward movement to said second position;
f) latching means releasably retaining said conducting member in said first position; and
g) actuating means for releasing said latching means to permit said biasing means to move said conducting member to said second position in response to a pre-determined fault condition in said electrical circuit.
The structure described in the specification for performing the function of “releasably retaining [the] conducting member in [the] first position” was a pin passing through a hole. The defendant instead used a magnet to perform this function. The ITC found the magnet to be an equivalent structure for performing the function.
The Federal Circuit reversed, relying on a previous case, holding as a matter of law that a structure that performs a function mechanically does so in a substantially different way from a structure that accomplishes the function with magnetic force. Thus, the claim was not infringed by the defendant’s device.
Judge Newman dissented on this issue, correctly pointing out that equivalence is a question of fact, not law as ruled on by the majority. The ITC’s determination of equivalence was supported by substantial evidence of experts who testified on the known interchangability of the two types of latches at the time of the filing of the ‘398 patent.
This is another case where the court’s opinion, substituting its judgment and understanding of factual evidence for that of the ITC, is difficult to grasp. There is, however, a definite lesson. Unless it is very difficult to draft a claim in any other way, avoid means-plus-function claim limitations. The court has made it clear that it will go out of its way to find such claims invalid or not infringed. These limitations have very little to no benefit and a very high risk.