Means-plus-function clauses in patent claims: a tortuous path.

• Author: Bradley, Charles W.

1. INTRODUCTION

   In 1952, the long efforts of the patent bar resulted in a new Patent Act that, with some changes, remains the statute that creates and controls patent rights. (1) The Patent Act of 1952 did not change the rule that the claims of a patent fix the boundary of what the patent covers. (2) One of the Act's more important provisions, then new to patent law, sought to provide a statutory basis for the use of so-called means-plus-function clauses in patent claims. (3) The new section provided:

   An element in a claim for a combination may be expressed as a means or step for performing a specified function without the recital of structure, material, or acts in support thereof, and such claim shall be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof. (4) This "means" provision allowed patentees to claim an element of a combination by what it does, rather than what it is.

   Means-plus-function clauses had been used in patent claims for many years before the passage of the Act. (5) In 1946, however, the Supreme Court held that a claim with such a clause at the point of novelty was indefinite. (6) The Court in Halliburton invalidated the claim because it purported to cover every means for performing the stated function. (7)

   In response to the decision, Congress enacted the above provision, now codified as § 112, paragraph 6, to authorize the use of means-plus-function clauses, while limiting the meaning ascribed to such clauses. (8) Congress provided that such clauses can be used in claims to a combination of elements, (9) which encompasses virtually all claims. When so used, the means element "shall be construed to cover the corresponding structure ... described in the specification [of the patent] and equivalents thereof." (10) This provision was merely an application of the so-called doctrine of equivalents to the means-plus-function arena. It required a determination of what structure in the specification of the patent performs the claimed function and whether the accused device contains that structure or an equivalent.

   However, the courts have inexplicably held that § 112, paragraph 6, concerns a different type of equivalence than the traditional doctrine of equivalents. (11) As a result, a jury in one case found that there was no equivalence under § 112, paragraph 6, but that there was equivalence under the doctrine of equivalents, (12) which led one judge to observe that the difference between these two concepts of equivalence escaped him. (13)

   While the effects of this purported difference appear to be diminishing, it is time for the courts to return to what Congress provided and remove the remaining aberrations that this detour has produced.

2. UNDERSTANDING THE STATUTE

   The wording of § 112 is not complex. In a 1963 opinion, Judge Rich, one of the drafters of the Act, quoted from a Patent Office Board of Appeals opinion describing the third paragraph of § 112 "to be so clear as not to require any resort to extrinsic evidence in connection with its interpretation." (14) In short, Congress spoke clearly and issued a clear mandate, which the courts must apply. (15) The mandate requires determining what structure in the specification of the patent performs the claimed function and determining whether the accused device contains that structure or an equivalent.

   However, the Federal Circuit decided that the term "equivalents," as used in § 112, paragraph 6, has a different meaning than it does under the traditional doctrine of equivalents. (16) Further, it held that § 112, paragraph 6, deals only with literal infringement, and that if § 112, paragraph 6, equivalence is not found in an accused device, one must proceed to consider whether equivalence is present under the doctrine of equivalents. (17) Thus, a two-step analysis arose. However, the difference between these equivalences is indefinable, and § 112, paragraph 6, suggested no such two-step analysis. These rulings raised questions concerning how the two equivalency standards differ and under what circumstances a patentee that has failed to establish infringement under the § 112, paragraph 6, standard can proceed to the traditional doctrine of equivalents standard.

   The Federal Circuit also decided that the equivalence test mandated by § 1 12, paragraph 6, is inapplicable when an accused device does not perform precisely the same function that appears in the claim. (18) However, the statutory mandate of how means clauses are to be construed is not dependent on what a putative infringer may be doing. The statute does not say, "Use this construction only if the accused device performs the precise function in the claim." Instead, once the function-performing structure in the specification of the patent has been identified, the issue is whether the accused device employs that structure or an equivalent. (19) If the relevant structure in the accused device performs a different function from the one recited in the means-plus-function clause, that factor should be considered in determining whether structural identity or § 112, paragraph 6, equivalence is present. The test, as mandated by paragraph 6, should still require a determination of (1) what structure in the specification performs the function claimed and (2) whether that structure or an equivalent structure is present in the accused device. (20)

   The various diversions from this course have resulted from the failure of the courts to pursue the path set by Congress. The correct path follows from the clear language of the Act, and it is consistent with the relevant history in the field of patent law.

3. PRIOR CASE LAW

   Long before the 1952 Patent Act, courts considered patent claims that recited various elements and concluded with the phrase "substantially as described" or "substantially as set forth." (21) The Supreme Court held that these phrases require reference to the patent specification and held that such claims cover the corresponding structure described in the specification and its equivalents. (22) For example, in ruling on such a claim, the Supreme Court held:

   Although the claims of the Winters and Crampton patent are limited to the structure therein disclosed, we find that they are infringed by the device of the Dent latch.... Except where form is of the essence of the invention, it has little weight in the decision of such an issue; and, generally speaking, one device is an infringement of another "if it performs substantially the same function in substantially the same way to obtain the same result." (23) The Court identified the corresponding structure in this case and applied the doctrine of equivalents. (24) The same methodology should follow in interpreting means-plus-function clauses under § 112, paragraph 6.

   Even more pertinent to the present discussion is the Supreme Court's pre-1952 discussion of a means-plus-function clause in Continental Paper Bag. (25) The means-plus-function clause at issue, as in Halliburton, was at the precise point of novelty. (26) It was argued that this means clause could be construed either to cover the corresponding structure in the specification and its equivalents (a harbinger of § 112, paragraph 6), or to cover every means that performs the recited function. (27) With regard to the first alternative, the Court stated:

   [I]t is argued that neither claim designates "operating means," either by names or by reference letters or numerals, and recourse must therefore be had to the descriptive part of the specification to ascertain what "operating means" are meant, and then construe the claim as calling for those "operating means" or their equivalents. (28) The invention in Continental Paper Bag Co. was a bag-making machine in which the structure in the patent that corresponded to the claimed "operating means" was a plate that oscillated about one of its edges and had its opposite edge abutting a rotating cylinder. (29) As described in the patent, the oscillating plate was mounted to move away from the cylinder as it oscillated. (30) The accused machine achieved the same result in a different way. (31) It employed an oscillating plate and rotating cylinder, but mounted the rotating cylinder so that it moved away from the oscillating plate, rather than having an oscillating plate that moved. (32) The Court compared the corresponding structure in the specification (which included the moving plate) with the relevant structure in the...