Note: This page is fairly long because patent infringement is a complicated topic.
Patent infringement generally falls into two categories: literal infringement and infringement under the doctrine of equivalents. The term "literal infringement" means that each and every element recited in a claim has identical correspondence in the allegedly infringing device or process. However, even if there is no literal infringement, a claim may be infringed under the doctrine of equivalents if some other element of the accused device or process performs substantially the same function, in substantially the same way, to achieve substantially the same result. This "expansion" of claim coverage permitted by the doctrine of equivalents, however, is not unbounded. Instead, the scope of coverage which is afforded the patent owner is limited by (i) the doctrine of "prosecution history estoppel" and (ii) the prior art.
An infringement analysis determines whether a claim in a patent literally "reads on" an accused infringer's device or process, or covers the allegedly infringing device under the doctrine of equivalents. The steps in the analysis are:
1. Construe the scope of the "literal" language of the claims.
2. Compare the claims, as properly construed, with the accused device or process, to determine whether there is literal infringement.
3. If there is no literal infringement, construe the scope of the claims under the doctrine of equivalents.
The doctrine of equivalents is an equitable doctrine which effectively expands the scope of the claims beyond their literal language to the true scope of the inventor's contribution to the art. However, there are limits on the scope of equivalents to which the patent owner is entitled.
In order to determine the scope of equivalents to which the patent owner is entitled, the doctrine of prosecution history estoppel must be considered. Prosecution history estoppel limits the scope under the doctrine of equivalents by preventing a patent owner from recapturing during litigation that which was given up during prosecution of the patent to avoid prior art and obtain a patent. This portion of the analysis is performed by obtaining and studying the patent application file.
Also, the scope of equivalents to which the patent owner is entitled is bounded by the prior art. The patent owner cannot expand the claims for purposes of finding infringement if the scope of equivalency sought would ensnare the prior art. Therefore, if infringement under the doctrine of equivalents is found, a prior art search should be performed to determine if the scope of equivalency ensnares the prior art.
B. Liability for Infringement
The definition of "patent infringement" can be found in 35 U.S.C. § 271(a) which defines direct infringement simply as the making, using or selling of a patented invention in the U.S. without authority from the patent owner. In addition, 35 U.S.C. § 271(b) extends liability for infringement to those who "actively induce" another to infringe a patent, and 35 U.S.C. § 271(c) extends liability to contributory infringers as follows:
"whoever sells a component of a patented machine, manufacture, combination or composition, or a material or apparatus for use in practicing a patented process, constituting a material part of the invention, knowing the same to be especially made or especially adapted for use in an infringement of such patent, and not a staple article or commodity of commerce suitable for substantial non-infringing use, shall be liable as a contributory infringer".
Any person or entity who is found liable for patent infringement is subject to the imposition of damages and an injunction. The damages to which a patent owner is entitled are the patent owner's lost profits as a result of the infringement, but not less than a reasonable royalty. In addition, if infringement is determined to have been willful, the court may award up to treble the actual damages and attorneys fees.
C. Claim Interpretation.
Generally speaking, terms are given their plain meaning, except to the extent that the inventor has chosen to be his own lexicographer and give a term a special meaning. This can be determined by examining the specification.
However, claim language can be cast in what is called "means plus function" form permitted under 35 U.S.C. §112, sixth paragraph, which provides that,
"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." (emphasis added).
By its express terms, therefore, Section 112, ¶6 permits an element in a claim to be expressed as a means or step for performing a specified function. However, the scope of such a claim is not limitless, but is confined to structures expressly disclosed in the specification and corresponding equivalents. Therefore, the statutory provision prevents an overly broad claim construction by requiring reference to the specification, and at the same time precludes an overly narrow construction that would restrict coverage solely to those means expressly disclosed in the specification.
In other words, a "literal" construction of such a limitation may encompass only the disclosed structure and its equivalents. Thus, the "plain meaning" of such a claim, without resort to limiting features contained in the specification, the prosecution history, and a factual inquiry into equivalents, might create an erroneously broad scope.
Therefore, arguments made during the prosecution history are relevant in determining the meaning of the terms at issue. The prosecution history of a patent contains:
"... all express representations made by or on behalf of the applicant to the examiner to induce a patent grant... Such representations include amendments to the claims and arguments made to convince the examiner that the claimed invention meets the statutory requirement of novelty, utility, and non-obviousness. Thus, the prosecution history (or file wrapper) limits the interpretation of claims as to exclude any interpretation that may have been disclaimed or disavowed during prosecution in order to obtain claim allowance."
In addition, the prosecution history of a parent case, and the construction of a term contained therein, is relevant to an understanding of that term as it is used in a continuation case.
Also, although a patentee may be his own lexicographer, the patent specification must support his asserted definition. Furthermore, terms of a claim must be interpreted with regard to the other claims, the specification, and the prosecution history. It is also important to note that the Federal Circuit has been consistent and uniform in its application of the law in this area, and has evidenced a liberal, pro-patent point of view.
D. Literal Infringement.
As indicated above, infringement of a claim requires that the accused device meet every limitation of the claim, either literally or under the doctrine of equivalents. In the case of literal infringement, if a claimed element is missing, then literal infringement is avoided. In other words, a "literal" construction of such a limitation may encompass only the disclosed structure and its equivalents.
In the case of a claim with a "means plus function" element, the element is met literally when (i) an accused device performs the same function recited in the element, and (ii) the accused device embodies the corresponding structure, material, or acts described by the specification or an equivalent thereof. 35 U.S.C. § 112, ¶6 provides that claim limitations "expressed as means ... for performing a specified function without the recital of structure ... in support thereof, ... shall be construed to cover corresponding structure ... described in the specification and equivalents thereof." In this paragraph (6) Congress sought to provide instruction on the interpretation of "means" claims, which otherwise might be held to be indefinite. Therefore, Paragraph 6 operates to cut back on the type of means which could literally satisfy the claim language. More specifically, where a claim sets forth a means for performing a specific function, without reciting any specific structure for performing that function, the structure disclosed in the specification must be considered, and the patent claim construed to cover both the disclosed structure and equivalents thereof.
E. Infringement Under the Doctrine of Equivalents.
One of the principal concerns with relying on the literal language of the claims in a patent is that, even though you avoid literal infringement, you may still infringe the patent under the "doctrine of equivalents." The "doctrine of equivalents" is a judicially created doctrine having a three part "function/way/result" substantial identity test embodying the following steps:
1. Determine whether the accused device or process achieves substantially the same result as the claimed invention. If it does not, the infringement inquiry ends.
2. Determine whether the accused device or process performs substantially the same function as the claimed invention. If it does not, the infringement inquiry ends.
3. Determine whether the accused device or process operates in substantially the same way as the claimed invention. If it does not, the infringement inquiry ends.
In applying this test, each element of the claim must also be compared with the accused device or process to determine whether the accused device or process contains each element or its substantial equivalent.
A substantial equivalent of an element is one that causes the accused device or process to operate in substantially the same way as the claimed invention, considering the nature, purpose and quality of the element and its corresponding structure in the accused device or process.
Another way of looking at this test is to determine if the differences between the claimed invention and the accused device are so insubstantial that a fraud on the patent would result. This occurs when, for example, changes are made solely to avoid the literal language of the claim, and the changes reflect little or no advantage.
In short, in order to find infringement under the doctrine of equivalents, an element-by-element comparison and not a "claim as a whole analysis", must be made between the claimed invention and the accused device. In determining if a "substantial equivalent" exists for a claimed element or limitation, the three-prong test can be used. However, even if a "substantial equivalent" can be found, there still can be no infringement if the asserted scope of equivalency would encompass the prior art or be barred by the prosecution history of the patent.
Note that the doctrine of equivalents presents a less demanding standard than that for literal infringement. For literal infringement there must be identity of elements; for the doctrine of equivalents to apply, there is only a "substantial" identity requirement. In applying the test, however, two principles are clear -- first, a claim cannot be broadened so far as to read on the prior art, and second, a patentee cannot recapture what was given up during prosecution of the patent. In other words, the "expansion" of claim coverage permitted by the doctrine of equivalents is not unbounded. Instead, the scope of coverage which is afforded the patent owner is limited by (i) prosecution history estoppel and (ii) the prior art.
(1) Prosecution History Estoppel.
As indicated above, the essence of prosecution history estoppel is that a patentee should not be able to obtain, through the doctrine of equivalents, coverage of subject matter that was relinquished during prosecution to procure issuance of the patent. Further, the legal standard for determining what subject matter was relinquished is an objective one, measured from the vantage point of what a competitor was reasonably entitled to conclude from the prosecution history, that the applicant gave up to procure issuance of the patent. Additionally, a patentee should not be able to obtain, under the doctrine of equivalents, coverage which he could not lawfully have obtained from the USPTO by literal claims.
(2) Effect of Prior Art.
A second limitation of the application of the doctrine of equivalents is the scope and content of the prior art. It is well established that the range of equivalents permitted under the doctrine of equivalents must not ensnare the prior art. The fundamental purpose of all such evaluations must be to prevent the patentee from obtaining, under the doctrine of equivalents, coverage which the patentee could not have obtained from the Patent and Trademark Office by literal claims.