Doctrine of Equivalence and prior history estoppel

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A patent is a monopoly right granted by a national or regional patent office to an inventor who has created something new, useful and non-obvious. Any invention demands huge investment of time, and resources in the form of research and development. Patent rights allow the owners to prevent others from exploiting their invention and allows them a fair return on their investment. The patent laws require inventors to describe their work in "full, clear, concise, and exact terms," thus maintaining the balance between the inventor’s interest and public interest.


At times, an imitation of the patent might not be a literal imitation but may provide the same effect. If such an imitation is allowed, it would defeat the purpose of granting the patent rights to the inventor. It would become more lucrative to make insignificant changes to the patent, assert that it does not fall within the literal language of the claims and enjoy larger returned than the original inventor without expending much effort or resources. It was to counter such behaviour that the Doctrine of Equivalence was evolved by the US state Supreme Court in Winans v. Denmead. The court ruled that infringement may occur even though the literal language of the claims was avoided.

Doctrine of Equivalents – Meaning/Definition

Patent infringement can take two forms: literal infringement and infringement under the doctrine of equivalents. Literal infringement means each and every element of the claim has been imitated by the infringer. Infringement under Doctrine of Equivalents occurs when 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. The Doctrine was evolved by the US Supreme Court in Winans v. Denmead. The doctrine further received clarity in Graver Tank & Mfg. Co. v. Linde Air Products Co.

It was held that “Under this doctrine, an accused article or method that does not literally meet the limitations of a claim may nevertheless infringe. Thus, even if there is no literal infringement, infringement could be found under the doctrine of equivalents, if the accused article or method was equivalent to the claimed invention. The doctrine of equivalents has created a tension between two important public policies. One policy focuses on the importance of providing public notice as to what infringes, by requiring clear and distinct claims. The other policy focuses on the need to prevent an infringer from avoiding liability by merely playing semantic games or by making only minor changes in the accused article or method to avoid the literal language of the claims. The Doctrine of equivalents is limited by (i) the doctrine of "prosecution history estoppel" and (ii) the prior art.

Doctrine of prosecution history estoppel – Meaning

Prosecution history estoppel precludes a patentee from obtaining under the doctrine of equivalents coverage of subject matter that has been relinquished during the prosecution of its patent application. The U.S Supreme Court, in the case of Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., cemented the application of the doctrine. The decision in Festo, the doctrine of prosecution history estoppel can be summarized as follows: 1. Any narrowing amendment made to satisfy the requirements of the Patent Act may give rise to an estoppel; 2. An unexplained narrowing amendment is presumed to have been made to satisfy the requirements of the Patent Act; 3. An estoppel does not create an absolute bar to the application of the doctrine of equivalents; 4. The applicant is presumed to have surrendered the scope of protection between the claim before amendment and after amendment; 5. It is the applicant's burden to show that the particular equivalent in question was not surrendered.

ELEMENTS (Operations around the Globe)

• Operation of the Doctrine of equivalents in the U.S.A.

The evolution of this doctrine is credited to the case of Winans v. Denmead.The Supreme Court stated that a patent would be valueless if the defendant can simply change the form of the invention claimed. In Warner-Jenkinson Co. v. Hilton Davis Chemical Co. the Court then clarified and restricted the application of the doctrine of equivalents holding that: Each element contained in a patent claim is deemed material to defining the scope of the patented invention, and thus the doctrine of equivalents must be applied to individual elements of the claim, not to the invention as a whole. This restriction of the doctrine of equivalents is referred to as the all elements rule. The case of Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., cemented the application of the doctrine and how it is limited by the doctrine of prosecution history estoppel. In its early development, the doctrine was usually applied in cases involving devices where there was equivalence in mechanical components. Subsequently, however, the same principles were also applied to compositions, where there was equivalence between chemical ingredients. Today the doctrine is applied to mechanical or chemical equivalents in compositions or devices.

• Operation of the Doctrine of equivalents in the U.K.

The UK allegedly does not follow this doctrine but treats “non literal” infringement cases by simply resorting to what they creatively call “purposive construction”.

• Operation of the Doctrine of equivalents in the India

The case which brought forward the doctrine in India was Ravi Kamal Bali vs Kala Tech AndOrs. The plaintiff, instituted an infringement suit seeking an interim injunction restraining Kala Tech, the defendant, from making, using, selling or distributing tamper proof locks/seals as it would be the infringement of his patent. He contended that Kala Tech’s product do the same work, in substantially the same way and accomplishes substantially the same result thereby contributing to the infringement. He also submitted that while considering the question of infringement of patents, the Court ought to apply the doctrine of equivalence by which a device is set to infringe a claim if it "performs substantially the same function in substantially the same way to obtain the same result". Although the interim injunction was not granted the importance of the case lies in in that, it was the first case where the doctrine was discussed in India.

Problems associated with the doctrine

Despite the doctrine having been around for 150 years a precise, settled, linguistic framework It is yet to evolve. This lack of a proper framework creates ambiguity and difficulty in application. When applied too broadly it interferes with the public notice function of the statutory claiming requirements. If a member of the public, after reviewing the patent creates a product that falls outside the literal scope of the claims of the patent and is later found to have infringed the same patent under the doctrine of equivalents, then the notice function served by the claims has failed. It has been a common concern that those who were genuinely trying to design around an invention and thought in good faith that they had successfully done so can be held for infringement under the doctrine. Another view that exists is that the modern doctrine of equivalents that protects inventions beyond the interpreted scope of claim language is not needed for fairness or efficiency and should be abolished. The fairness arguments lack theoretical justification, the doctrine imposes high social costs and likely impedes innovation, and doctrine of equivalents needlessly conflicts with other patent law doctrines and unduly complicates patent litigation procedures. Despite the associated drawbacks the importance of the doctrine in ensuring the inventors their fair share cannot be overlooked. The courts in the U.S.A .have ensured proper application of the doctrine by developing various limitations. If the doctrine subject to limitations is derived into the Indian scenario it would be enormously beneficial.

Famous cases

1. Warner-Jenkinson v. Hilton Davis Chemical Co. —

The case established the "all elements" rule. This rule states that each claim element must be examined instead of the whole invention. Every element of the original invention must have an equivalent in the infringing invention for a claim to stand. The elements of the patented invention must have substantial equivalents in the new invention. This means they meet the rules of the triple identity test. If an element is missing, it will only be equivalent if there are superficial differences in the infringing device. Equivalency should only be examined after a claim has been filed. It should not occur when an invention is patented. New technology developed after patenting may change the nature of essential elements.

2. Brilliant Instruments v. GuideTech case.

In this case, a former GuideTech worker started his own company. GuideTech sued him for infringement on one of their products. The initial ruling went in the employee's favor. However, the Supreme Court decided that the DOE applied in this case and that the employee was guilty of infringement. In the case, the employee redesigned a circuit commonly used by GuideTech. While the design was different, it functioned in the same way. This constituted infringement. If an invention works the same way, even if it is not designed the same, infringement has usually happened.

3. Akzo Nobel Coatings, Inc. v. Dow Chemical Company case

In the case, the court examined two methods for handling dispersion in pipes. Akzo, the patent holder, lost his initial claim and appealed. The Federal Circuit found that Akzo did not prove that his invention functioned in substantially the same way as the defendant's. This decision shows that vitiation may be a legitimate defense. If the patent holder cannot prove that his device functions in an equivalent way to the defendant's, there is no infringement.

4. In Intendis GMBH v. Glenmark Pharmaceuticals Inc., USA Glenmark Pharms Inc.

Bayer made a gel that treated a skin condition. The gel was covered by the '070 patent. Glennmark made a generic gel and claimed the patent didn't apply. This claim was based on the fact that the generic gel contained different inactive ingredients. Another item in question was the lecithin content. Glennmark claimed their gel contained no lecithin. The court ruled that this could not be proven. Therefore, Glennmark's product contained the same ingredients as Bayer's.

The court found that DOE applies even if the patent does not spell out function, way, and result. Because the Glennmark gel performed the same function as the Bayer gel and their ingredients were not substantially different, it was ruled that DOE applied. This case shows that DOE applies even if a patent is limited in its descriptions. Making minor changes to a product does not invalidate patents. DOE still applies.

5. Sporting Goods v. David Geoffrey & Assoc.

The case decision established hypothetical claims. This process was refined in Ultra-Tex Surfaces, Inc. v. Hill Bros. Chem. Co. and Streamfeeder, LLC v. Sure-Feed Systems, Inc.

The question in the Ultra-Tex case involved a process for creating concrete surfaces. Ultra-Tex claimed its process, which used a polycot paper was infringed upon by the Hill Bros. process, which used heavy wax impregnated paper. To prove infringement, Ultra-Tex used a hypothetical claim. However, in the claim, they both broadened the hypothetical claim so that it would cover the product in question and added limitations to avoid prior art. The court decided it was improper to broaden and narrow the claim for a hypothetical. The court removed the limitations and focused on the broadened claim. Because that claim would cover prior art as well as the product in question, their claim of infringement was denied. The Streamfeeder decision imposed procedural limits. The court found that the burden of proving the hypothetical claim rests with the patent holder. However, once the hypothetical claim has been allowed, the burden shifts to the defendant. The defendant must show that the claim would not be granted based on prior art.


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