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Doctrine of Equivalents

Posted Friday, February 24, 2012 by Mike Cicero

Specific language that is used to define rights and duties is often very important to people who wish to deliberately and rationally plan their actions. Thus, in some situations immense effort is expended towards understanding and arguing over the precise meaning of such language. The tax code is a prime example of such language because it is incredibly complicated and, depending on how well it is navigated, it is potentially incredibly burdensome. The language of patents is also hugely important. The claims are the part of a patent that provide the legal definition of the patentee’s monopoly. Accordingly, the precise meaning of patent claim language has been intensely debated for centuries.

Historically, patent claims were interpreted through the use of literalism which means to that the explicit substance of the patent claims was adhered to when interpreting claims. Because claim interpretation defines the scope of patent protection huge amounts of effort have been, and continue to be, expended towards drafting sufficiently broad claims. On the opposite side, skilled practitioners seek to discover and exploit loopholes which claim language might fail to cover.

Take for example the common need of having a drive shaft provide power to an input shaft of some sort. There are many known ways to accomplish this and so in drafting the claims a practitioner would likely avoid describing the system with exactitude. Instead, the claims might be drafted such that the drive shaft is coupled to the input shaft. The term coupled might seem like it is sufficiently broad to provide a meaningful monopoly. However, one could reasonably interpret the term coupled to require a mechanical connection between the two shafts. Suppose now that a competitor begins to sell an identical product except for one difference; the competitor substitutes a magnetic means to transfer power in place of the mechanical connection. (Local company MagnaDrive produces such magnetic power transfer systems). Will the competitor escape infringement liability due to what could be an immaterial variation of the invention? Maybe not. Under certain limited circumstances, the United States patent system allows a patentee to extend patent protection beyond what is literally claimed.

The doctrine of equivalents allows patent protection to be extended beyond what is literally recited in the claims to something which is substantially equivalent to the claimed invention. A famous judge and patent lawyer, Learned Hand J., once stated that the purpose of this doctrine was “to temper [cruel] logic and prevent an infringer from stealing the benefit of the invention.” Royal Typewriter Co v. Remington Rand Inc., 168 F.2d 691, 692 (1948). Under the doctrine of equivalents, whether the competitor will escape infringement liability depends on whether the difference between the limitation of claimed invention and the accused infringing invention is insubstantial. Warner-Jenkinson Company, Inc. v. Hilton Davis Chemical Co., 520 U.S. 17, 117 S.Ct. 1040 (1997). The Supreme Court has held that a patentee may invoke the doctrine of equivalents against an accused infringer if the accused is performing “substantially the same function in substantially the same way to obtain the same result” as the claimed invention. Graver Tank & Mfg. Co. v. Linde Air Products Co., 339 U.S. 605, 608, 70 S.Ct. 854 (1950). This is one of many articulations of what constitutes an insubstantial difference.

Returning to the hypothetical with the magnetic power transferring system, certainly more information about the inventions would be needed to perform a thorough analysis. Even then an answer could not be provided with perfect certainty unless the issue was litigated. However, the outcome would depend on two issues. The first issue that would be decided would be whether the magnetic means to transfer power is in fact a coupler. If the court decides that it is then the patentee would be protected. However, if it is not the patentee may attempt to invoke the doctrine of equivalents and extend the patents protection beyond the literal claims. Then the issue would be whether the difference between the claimed invention, with the shafts coupled, and the accused infringing invention using the magnetic means is insubstantial. If the court decides it is, then the patentee would be in luck.

Doctrine of Equivalents ›› Ruttler Mills PLLC