Without a Net: the Supreme Court Attempts to Balance Patent Protection and Public Notice in Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co

Publication year2001


Creighton Law Review

Vol. 36

"Each case is inevitably a matter of degree, as so often happens, and other decisions have little or no value."(fn1)

"No doubt, this is, strictly speaking an anomaly; but it is one which courts have frankly faced and accepted almost from the beginning."(fn2)


The United States Constitution provides for a patent system by granting Congress the power "[t]o promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writing and Discoveries."(fn3) The goal of the patent system is to promote innovation, which consequently contributes to economic growth.(fn4) The patent system achieves this goal by creating an incentive to invent through the grant of a limited monopoly.(fn5) To receive the protection afforded by the patent system, inventors must disclose their innovations to the public.(fn6) The disclosure of inventions furthers innovation in a second way by allowing competitors to build upon the discoveries encompassed in patented inventions.(fn7) Accordingly, the United States' patent system furthers the goal of encouraging innovation in at least two ways: (1) providing protection to patented inventions and (2) giving public notice of new technologies.(fn8)

The scope of protection afforded to a patent holder is determined by the patent's claims.(fn9) Because the limitations of language make it virtually impossible to perfectly describe a new technology, literal construction of patent claims would significantly decrease the protection afforded to patented inventions.(fn10) Therefore, courts developed what is now referred to as the doctrine of equivalents, which allows courts to broaden the scope of a patent to extend beyond the literal language of the claims.(fn11) The doctrine of equivalents allows a patentee to find infringement in a competitor's product that substantially performs the same function, in the same way, with the same result.(fn12) Accordingly, the doctrine serves to protect patents from unscrupulous copyists who could otherwise make insignificant and unimportant changes to an invention to circumvent the patent system.(fn13)

Because the doctrine of equivalents allows for a construction of patent claims beyond their literal interpretation, the doctrine is in tension with the fundamental principle that the patent claims measure the extent of the patent's protection.(fn14) Accordingly, courts have been concerned with an unbridled application of the doctrine that conflicts with the public notice function of patent law.(fn15) Therefore, courts have developed a number of restraints to the doctrine, such as prosecution history estoppel.(fn16) Prosecution of a patent is the examination procedure carried out by the Patent and Trademark Office ("PTO"), and the prosecution history of a patent is the record of the interaction between an applicant and the PTO prior to issuance of a patent.(fn17) Prosecution is typically an iterative process between the two parties, and the patent claims are usually amended during the process.(fn18) Under prosecution history estoppel, a patentee cannot later capture an equivalent to an amended claim under the doctrine of equivalents if the subject matter was relinquished during the prosecution of the patent.(fn19)

The doctrine of equivalents and prosecution history estoppel compete to protect different interests of the patent system.(fn20) The doctrine of equivalents ensures that patented inventions are adequately protected.(fn21) On the other hand, a rigid application of prosecution history estoppel favors the public notice function.(fn22) The strength of the patent system relies upon the proper balance between patent protection and public notice.(fn23) Therefore, courts have struggled in the application of the competing doctrine of equivalents and prosecution history estoppel in an attempt to balance the competing interests of patent protection and public notice.(fn24)

Recently, in Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co. (Festo VII),(fn25) the United States Supreme Court once again addressed the relationship between the two competing patent law concepts, the doctrine of equivalents and prosecution history estoppel.(fn26) In particular, the Court focused on two questions.(fn27) First, the Court examined the question of what types of amendments to patent claims give rise to prosecution history estoppel, finding that estoppel applies when an amendment narrows a patent's scope and was necessary to secure the patent.(fn28) Second, the Court addressed the question of whether any scope of equivalents remains for an amended claim, rejecting the United States Court of Appeals for the Federal Circuit's adoption of a complete bar rule.(fn29) Instead, the Court indicated that amendments that give rise to prosecution history estoppel create a presumption that the amendment surrendered all equivalents.(fn30) The Court held that in order to rebut this presumption, a patentee must show that the amendment did not surrender a particular equivalent by demonstrating that "one skilled in the art could not reasonably be expected to have drafted a claim that would have literally encompassed the alleged equivalent."(fn31)

This Note will first review the facts and holding of Festo VII.(fn32) Next, this Note will examine the Supreme Court's historical progression and development of the doctrine of equivalents and prosecution history estoppel.(fn33) This Note will then argue that the Court's decision expanded the types of amendments that give rise to prosecution history estoppel, emphasizing the public notice interests.(fn34) Next, this Note will discuss the Court's rejection of the Federal Circuit's complete bar application of prosecution history estoppel and opine that the rejection restored some balance between patent protection and public notice.(fn35) This Note will then discuss the scope of equivalents remaining for amended claims under the Court's new rebuttable presumption in Festo VII.(fn36) Finally, this Note will argue that although the Supreme Court intended to balance the competing interests of patent protection and public notice, the Court's decision will result in very minimally increased certainty at the expense of reduced protection for inventions.(fn37)


Festo Corporation ("Festo") is the owner of two patents, United States Patent No. 3,779,401 (the "Carroll patent") and United States Patent No. 4,354,125 (the "Stoll patent"), which relate to a magnetically coupled rodless cylinder.(fn38) The device has a wide range of uses and has been "employed in machinery as diverse as sewing equipment and the Thunder Mountain ride at Disney World."(fn39) After Festo started selling the device, Shoketsu Kinzoku Kogyo Kabushiki Co. ("SMC") began selling a similar device, although SMC's device was not identical to the inventions disclosed by Festo's two patents.(fn40) SMC's device has two notable differences from the claims of the Festo inventions.(fn41) First, rather than using a pair of one-way sealing rings, SMC's device utilizes a single two-way sealing ring.(fn42) Second, the outer portion of the sleeve of the SMC device is made of a nonmagnetizable alloy.(fn43) The Carroll patent had been amended during a reexamination proceeding to include the limitation that the device contains a pair of sealing rings.(fn44) The Stoll patent had been amended during the prosecution of the patent to include both the sealing ring and magnetizable material limitations.(fn45)

Festo sued SMC in the United States District Court for the District of Massachusetts for infringement of the patents (Festo I).(fn46) Because of the complexity of the claims, the court referred the case to a special master pursuant to Federal Rule of Civil Procedure 53.(fn47) On April 27, 1993, the special master issued his report.(fn48) In the report, the master concluded that the claims at issue of both the Carroll patent and the Stoll patent were valid.(fn49) The special master also concluded that the SMC device infringed the Carroll patent under the doctrine of equivalents.(fn50) However, the master determined that the prosecution history of the Stoll patent estopped Festo from asserting that the Stoll patent was infringed under the doctrine of equivalents.(fn51)

Following the master's report, the parties made various motions.(fn52) The district court allowed Festo's motion for partial summary judgment with respect to the Carroll patent, finding that SMC infringed the patent pursuant to the doctrine of equivalents.(fn53) The court, however, declined to adopt the special master's recommendation that prosecution history estoppel barred Festo from asserting infringement of the Stoll patent under the doctrine of equivalents.(fn54) The court indicated that there existed a disputed factual issue appropriate for a jury and denied both Festo's and SMC's motions for sum-mary judgment with respect to the Stoll patent.(fn55) After trial of the remaining issues, the jury found both the Carroll patent and the Stoll patent valid, found that SMC had infringed the Stoll patent under the doctrine of equivalents, and assessed damages.(fn56)

On appeal before the United States Court of Appeals for the...

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