Using the Doctrine of Equivalents to Determine Infringement

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Using the Doctrine of Equivalents to Determine Infringement

“If two devices do the same work in substantially the same way, and accomplish substantially the same result, they are the same, even though they differ in name, form, or shape.” This excerpt from a 1950 U.S. Supreme Court decision (Graver Tank & Mfg. Co. v. Linde Air Products Co.) defines the essence of the doctrine of equivalents.

Although the wording is simple, the application of the doctrine of equivalents to individual cases can be complex. Determining equivalency often relies on differing opinions by scientists or other experts as to certain scientific facts, and the outcome of a case may rest on which expert is the most believable.

While a patent has several elements — a specification, drawings, and one or more claims — it is only patent claims that can be infringed, so a court will examine the claims of the patent in question closely. All claim requirements will be scrutinized to determine if each element set forth in the claim also appears in the accused product or process. Sometimes the infringement will be obvious. However, more often there are differences that require further review. An accused infringer may have been aware of the existing patent and taken steps to avoid infringement by making changes from what is claimed in the patent. When this occurs, the issue of equivalency arises.

Courts use two tests for determining infringement under the doctrine of equivalents:

  1. Function-Way-Result test is used to determine whether a potentially infringing product performs substantially the same function in substantially the same way to get the same result. This is typically used for mechanical patent infringement cases.
  2. Insubstantial Differences test is used to determine if the potentially infringing product is substantially different that the patented product. This test is typically used for non-mechanical patents.

Even if a product is not exactly the same as a patented product — or is missing an element of a patented claim — it is still possible for infringement to occur under the doctrine of equivalents. The burden of proof in a patent infringement lawsuit rests with the patent holder, who must prove by the greater weight of evidence (“preponderance of evidence” standard) that the patent has been infringed.

Intellectual property law is complex. Skilled representation is necessary. Williams Mestaz, L.L.P., is a law firm with decades of experience in commercial litigation, including IP infringement, employee lawsuits, business divorce, aviation, and high stakes litigation. Contact us at (602) 256-9400 and schedule a time to meet with us today.

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