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infringement of a patent

Claim Interpretation
Doctrine of Equivalence



Infringement of a patent consists of the unauthorized making, using, offering for sale or selling any patented invention within the United States or United States Territories, or importing into the United States of any patented invention during the term of the patent. If a patent is infringed, the patentee may sue for relief in the appropriate Federal court. The patentee may ask the court for an injunction to prevent the continuation of the infringement and may also ask the court for an award of damages because of the infringement. In such an infringement suit, the defendant may raise the question of the validity of the patent, which is then decided by the court. The defendant may also aver that what is being done does not constitute infringement. Infringement is determined primarily by the language of the claims of the patent and, if what the defendant is making does not fall within the language of any of the claims of the patent, there is no literal infringement.

Suits for infringement of patents follow the rules of procedure of the Federal courts. From the decision of the district court, there is an appeal to the Court of Appeals for the Federal Circuit. The Supreme Court may thereafter take a case by writ of certiorari. If the United States Government infringes a patent, the patentee has a remedy for damages in the United States Court of Federal Claims. The Government may use any patented invention without permission of the patentee, but the patentee is entitled to obtain compensation for the use by or for the Government.

The claims define the scope of protection for a patent afforded to the actual inventor. Patent law requires the applicant to swear, or affirm, that he believes himself to be the true inventor of the art, machine, or improvement, for which he asks for a patent; and further that he shall deliver a written description of his invention, in such full, clear, and exact terms, that any person, acquainted with the art, may know how to construct and use the same. The reason for this is to guard the public against unintentional infringements of the patent, and to enable the public to make an improvement that does not infringe your patent. When an accused device possess every limitation of a claim in your patent, then that device or process has comitted literal infringement of your patent. However, the language in the patent claims may not capture every nuance of the invention or describe with complete precision the range of its novelty. If patents were always interpreted by their literal terms, their value would be greatly diminished. Unimportant and insubstantial substitutes for certain elements could defeat the patent, and its value to inventors could be destroyed by simple acts of copying. For this reason, the clearest rule of patent interpretation, literalism, may conserve judicial resources but is not necessarily the most efficient rule. The scope of a patent is not limited to its literal terms but instead embraces all equivalents to the claims described. In this way, a balance between the two competing policies behind the enforcement of patent rights: (1) to protect the inventor’s right to exclude others who might steal the product of his work by making equivalent modifications, and (2) to provide clear notice to the public of the invention’s boundaries.

The Patent Office has no jurisdiction over questions relating to infringement of patents. In examining applications for patent, no determination is made as to whether the invention sought to be patented infringes any prior patent. An improvement invention may be patentable, but it might infringe a prior unexpired patent for the invention improved upon, if there is one.

Claim Interpretation 

For a patent to be enforced, the claims must be interpreted by the courts during infringement lawsuits.  The case law governing claim interpretation is very complex; however, some important aspects are discussed below. The purpose of claims is not to explain the technology or how it works, but to state the legal boundaries of the patent grant. A claim is not "indefinite" simply because it is hard to understand when viewed without benefit of the specification.

Claim interpretation is the process of giving proper meaning to the claim language. Claim language, after all, defines claim scope. Therefore, the language of the claim frames and ultimately resolves all issues of claim interpretation. In determining the meaning of disputed claim terms, however, a construing court considers the descriptions in the rest of the patent specification, the prosecution history, and relevant extrinsic evidence.

That is, a patent claim is construed by examining the claim in the context of the specification, drawing on the specification for an understanding of what is covered by the claim, and looking to the rejections, explanations, and revisions that comprise the record of the patent examination. The subject matter of the invention and its delineation in the claims is construed as it would be understood by persons knowledgeable in the field of the invention. Thus, a technical term is taken to have the meaning that it would ordinarily have in the field of the invention, unless it is shown that the inventor used the term with a special meaning and that persons of skill in the field would so understand the usage.

To learn the necessary context for understanding the claim language a construing court may consult other sources, including the patent specification, the administrative record of patent acquisition, expert commentary from those of skill in the art, and other relevant extrinsic evidence. In other words, a construing court does not accord the specification, prosecution history, and other relevant evidence the same weight as the claims themselves, but consults these sources to give the necessary context to the claim language.

The general rule is, that terms in the claim are to be given their ordinary and accustomed meaning. General descriptive terms will ordinarily be given their full meaning; modifiers will not be added to broad terms standing alone. In short, a court must presume that the terms in the claim mean what they say, and, unless otherwise compelled, give full effect to the ordinary and accustomed meaning of claim terms. In order to overcome this heavy presumption in favor of the ordinary meaning of claim language, case law makes clear that a party wishing to use statements in the written description to confine or otherwise affect a patent's scope must, at the very least, point to a term or terms in the claim with which to draw in those statements. That is, claim terms cannot, generally, be narrowed by reference to the written description or prosecution history unless the language of the claims invites reference to those sources. In other words, there must be a textual reference in the actual language of the claim with which to associate a proffered claim construction.

Case law demonstrates two main situations where a sufficient reason exists to require the entry of a definition of a claim term other than its ordinary and accustomed meaning. The first arises if the patentee has chosen to be his or her own lexicographer by clearly setting forth an explicit definition for a claim term. The second is where the term or terms chosen by the patentee so deprive the claim of clarity that there is no means by which the scope of the claim may be ascertained from the language used. For example, if a disputed claim term is a term with no previous meaning to those of ordinary skill in the prior art, its meaning, then, must be found elsewhere in the patent, whereby the specification is used for guidance when the meaning of a claim term is in doubt. The written description can supply understanding of unclear claim terms, but should never trump the clear meaning of claim terms. Hence, to avoid a potential limitation of claim scope, a claim term should not be so amorphous that one of skill in the art can only reconcile the claim language with the inventor's disclosure by recourse to the specification. In these two circumstances, a term or terms used in the claim invites or indeed, requires reference to intrinsic (i.e., the claims, the written description, and, if in evidence, the prosecution history) , or in some cases, extrinsic (e.g., treatises, technical references, and expert testimony), evidence. Reference to extrinsic evidence is generally proper when intrinsic evidence cannot resolve ambiguity in claim language, to determine the scope of the claim language.

The language in the patent claims may not capture every nuance of the invention or describe with complete precision the range of its novelty. If patents were always interpreted by their literal terms, their value would be greatly diminished. Unimportant and insubstantial substitutes for certain elements could defeat the patent, and its value to inventors could be destroyed by simple acts of copying. For this reason, the clearest rule of patent interpretation, literalism, may conserve judicial resources but is not necessarily the most efficient rule. The scope of a patent is not limited to its literal terms but instead embraces all equivalents to the claims described.

Doctrine of Equivalents 

The constitutional purpose of patent law is to "promote the Progress of Science and useful Arts" by granting inventors exclusive rights to their inventions for a limited period of time.  The judicially created doctrine of equivalents has long played an important, albeit controversial role in the realm of patent law.  It strives to strike a balance between the two competing policies behind the enforcement of patent rights: (1) to protect the inventor's right to exclude others who might steal the product of his work, and (2) to provide clear notice to the public of the invention's boundaries. 

The doctrine of equivalents is an equitable doctrine established by the courts to protect patented inventions.  In order to find that a patent has been infringed (literal infringement), every element of the patented claim must be found in the infringing device.  Thus, a copyist can avoid literal infringement by making changes so that his or her device does not have the exact elements disclosed in the patented claim.  Any discrepancy between the patented claim and the accused device will negate a finding of literal infringement. 

However, in order to protect patent owners from copyists stealing the patented invention by making small or insubstantial changes to the invention, the Supreme Court established the principle of infringement under the doctrine of equivalents.  This doctrine allows a court to find infringement if the elements of the accused device are "insubstantially" different from those disclosed in the patent. Hence, the doctrine of equivalents allows the patentee to claim those insubstantial alterations that were not captured in drafting the original patent claim but which could be created through trivial changes. When, however, the patentee originally claimed the subject matter alleged to infringe but then narrowed the claim in response to a rejection, he may not argue that the surrendered territory comprised unforeseen subject matter that should be deemed equivalent to the literal claims of the issued patent.

When the Court in Winans v. Deninead (15 How. 330, 343 (1854)) first adopted what has become the doctrine of equivalents, it stated that "[t]he exclusive right to the thing patented is not secured, if the public are at liberty to make substantial copies of it, varying its form or proportions." The debate continued in Graver Tank & Mfg. Co. v. Linde Air Products Co. (339 U.S. 605, 607 (1950)), where the Court reaffirmed the doctrine. Graver Tank held that patent claims must protect the inventor not only from those who produce devices falling within the literal claims of the patent but also from copyists who "make unimportant and insubstantial changes and substitutions in the patent which, though adding nothing, would be enough to take the copied matter outside the claim, and hence outside the reach of law." More recently, in Warner-Jenkinson, the Court reaffirmed that equivalents remain a firmly entrenched part of the settled rights protected by the patent.

Because of the inherent uncertainty in the doctrine of equivalents, courts have exercised their equitable powers to limit the doctrine. An important limit is the principle of prosecution history estoppels. This doctrine relates to the amendments, statements, arguments, and representations made by the patent applicant during the course of obtaining a patent. Any statement that limits the scope of the patent made for "a reason related to patentability" is binding and the applicant will be forbidden (estopped) from later attempting to argue that the limitation does not exist. 

The courts are continually struggling with the crucial issue of when should the doctrine of equivalents be applied, and at what point is the claim language of a patent stretched too far; Festo is only the latest case of many on this issue. 

Generally, a particular structure can be deemed outside the reach of the doctrine of equivalents because that structure is clearly excluded from the claims whether the exclusion is express or implied.

Courts generally recognize that their case law and reasoning places a premium on forethought in patent drafting, which may lead to higher costs of patent drafting and prosecution. However, in recent years, they consider that an alternative rule -- that is, allowing broad play for the doctrine of equivalents to encompass foreseeable variations, not just of a claim element, but of a patent claim -- also leads to higher costs. Society at large would bear these latter costs in the form of virtual foreclosure of competitive activity within the penumbra of each issued patent claim.

An accused device may infringe a claim under the doctrine of equivalents if it performs substantially the same overall function or work, in substantially the same way, to produce substantially the same overall result as the claimed invention. To be an equivalent, the element substituted in the accused device for the element set forth in the claim must not be such as would substantially change the way in which the function of the claimed invention is performed. Under the doctrine of equivalents, the accused device and the claimed invention cannot work in `substantially the same way' if a limitation (including its equivalent) is missing. Moreover, the doctrine of equivalents does not require a one to one correspondence between components of the accused device and the claimed invention. An accused device may infringe under the doctrine of equivalents even though a combination of its components performs a function performed by a single element in the patented invention. The accused device must nevertheless contain every limitation or its equivalent. Equivalency can also exist when separate claim limitations are combined into a single component of the accused device. One to one correspondence of components is not required, and elements or steps may be combined without ipso facto loss of equivalency. Each case must be decided in light of the nature and extent of the differences between the accused device and the claimed invention, on the equitable principles of the doctrine of equivalents. An "equivalent" of a claim limitation cannot substantially alter the manner of performing the claimed function. Where an accused device performs substantially the same function to achieve substantially the same result but in a substantially different manner, there is no infringement under the doctrine of equivalents.


A court case of Festo Corp. v. Shoketsu Kinzoki Kogyo Kabushiki Co (SMC Corp.), referred to as "Festo", has recently challenged prior doctrine of equivalence practice.  In this case Festo's patent claimed a device with a pair of sealing rings and the defendant's device only employed one sealing ring. In the court's view, such differences were insubstantial, and thus the court found the defendant liable for patent infringement under the doctrine of equivalents. 

The spirit behind the Festo decision is that patent laws "promote the Progress of Science and useful Arts" by rewarding innovation with a temporary monopoly. U. S. Const., Art. I, §8, cl. 8. The monopoly is a property right; and like any property right, its boundaries should be clear. This clarity is essential to promote progress, because it enables efficient investment in innovation. Moreover, a patent holder should know what he owns, and the public should know what he does not. For this reason, the patent laws require inventors to describe their work in "full, clear, concise, and exact terms," 35 U. S. C. §112, as part of the delicate balance the law attempts to maintain between inventors, who rely on the promise of the law to bring the invention forth, and the public, which should be encouraged to pursue innovations, creations, and new ideas beyond the inventor's exclusive rights.

Although both infringement under the doctrine of equivalents and prosecution history estoppels appear to complement one another, there are interesting questions regarding the interface between the two doctrines. For example, if an element has been limited by an amendment, is prosecution history estoppel a complete bar on all possible equivalents to this element, or is there a range of equivalents still available in an infringement analysis?  Moreover, is an equivalent structure discovered after the submission of the amendment also barred by prosecution history estoppel, or does the estoppel apply only to those equivalents specifically disclaimed in the amendment?  

Generally, practitioners should try to obtain allowance of claims that not only will satisfy a patent examiner, but also will be found both valid and infringed (and enforceable) in litigation.  The practitioner therefore should consider how courts likely will construe claims and what impact actions taken during patent prosecution likely will have on that construction.  In particular, Festo has placed a premium on obtaining valid and enforceable claims with a minimum of prosecution history.  In other words, practitioners should now also strive to draft original claims that are in condition for allowance without need for amendment.  This patent practice is in stark contrast to prior approaches that advised clients not to search too hard for prior-art, and started with weak initial claims that were expected to be amended to good form during prosecution. 

The courts conclusion that prosecution history estoppel arises when a claim is narrowed to comply with §112 gives rise to the second question presented: Does the estoppel bar the inventor from asserting infringement against any equivalent to the narrowed element or might some equivalents still infringe? The Court of Appeals held that prosecution history estoppel is a complete bar, and so the narrowed element must be limited to its strict literal terms. Based upon its experience the Court of Appeals decided that the flexible-bar rule is unworkable because it leads to excessive uncertainty and burdens legitimate innovation. For the reasons that follow, the court disagreed with the decision to adopt the complete bar. Though prosecution history estoppel can bar challenges to a wide range of equivalents, its reach requires an examination of the subject matter surrendered by the narrowing amendment.


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