What Is the Doctrine of Equivalents?

The doctrine of equivalents is a legal method for a patent owner to file an infringement claim even though the original product is not completely identical to the infringing product. 

There are a variety of ways for patent holders to protect their intellectual property. One of these methods is called the "doctrine of equivalents" (DOE). The doctrine of equivalents lets a patent holder sue for infringement if the product in question isn't exactly the same as the original. This prevents someone from making minor changes to a product in order to avoid an infringement case. 

In these cases, the Court will examine whether the infringing product is for the same purpose or completes the same function as the original product. If the product is found to be equivalent in these ways, then the patent holder will win their claim. 

This doctrine was established in Graver Tank & Mfg. Co. v. Linde Air Prods., Inc. The decision of this case resulted in the "triple identity" test. Under this test, a product is equivalent if it meets the following criteria:

  • It performs the same function as the original.
  • It performs that function in the same way.
  • It achieves the same result as the original.

A later Supreme Court case — Warner-Jenkinson v. Hilton Davis Chemical Co. — 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. 

Expanding Infringement

In the Warner-Jenkinson decision, the Court greatly narrowed what could be considered infringement. In the past, infringement was determined by the patent. After this decision, infringement cases are more restricted. Each element of an invention must be examined. No longer is an invention examined as a whole. 

An example of this is the 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. 

Vitiation Rule

In the DOE, there is something known as the vitiation rule. This rule is a common defense against a DOE claim used when two elementsare complete opposites. Vitiation prevents the DOE from being used to make a claim term meaningless. Vitiation applies when no reasonable jury could find two elements to be equivalent. In this case, the judge would make a complete or partial decision without sending it to a jury.

It doesn't matter if two elements are designed differently so long as the work the same way, as in the GuideTech case. For vitiation to apply, elements must be so different that there is no way equivalency could be established. If a judge cannot determine equivalency, the question will be left to the jury. 

Vitiation claims are seeing something of a comeback. The reason for this is that the Federal Circuit has placed the burden on patent holders. In the Akzo Nobel Coatings, Inc. v. Dow Chemical Company 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. 

Hypothetical Claim

One way for a court to determine DOE is using a hypothetical claim. A hypothetical claim determines whether a product has infringed on an existing patent by copying its prior art in such a way that consumers would assume it served the same function. An example of this can be found 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. 

Generally, there are three limitations on the doctrine of equivalents:

  1. The difference in the two inventions must be minor.
  2. Patent holders are limited by the claims in their patent.
  3. Equivalents cannot be used to encompass prior art.

Hypothetical claims are used to address the third limit. These claims examine whether an equivalent claimed by the patent holder would have been granted in their original patent. If not, it cannot be used in a DOE case. This serves three purposes. First, it prevents the defendant from dealing with an undue burden. Second, it protects inventions in the public domain. Third, it preserves the power of the Patent and Trademark Office to govern prior art. 

The decision in Sporting Goods v. David Geoffrey & Assoc. 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 polycoat 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.  

Amending Claims

It's common for a patent to be issued with different claims than the ones with which it was originally filed. Patents can be rejected multiple times. Claims must be adjusted to be both narrower and to provide more descriptive details. If a patent is denied on the basis of prior art and the applicant adjusts their claims to avoid this prior art, they cannot make broader claims. They gave up the broader claim to allow the narrower claims to be approved. This means they cannot state the narrow claims are the equivalent of the broad claim. 

The history of your claims being rejected and amended is recorded in a file maintained by the USPTO. This history will be stored in a large paper jacket that is called a "file wrapper." Because of this, the process of a claim being rejected and then being narrowed and refilled with a limiting amendment is called a "file wrapper estoppel."

Why Doctrine of Equivalents Is Necessary

Patents usually include the following parts:

  • Drawings of the invention
  • A specification
  • One or more claims

In an infringement case, the only part of the patent that matters is the claims. To determine infringement, each claim of the patent will be read and compared to the accused product. In most cases, infringement is clear. However, sometimes this is not the case. Sometimes, a person will incorporate differences into their invention to avoid infringement. These small differences can make infringement unclear, which is the purpose of the DOE. 

The reason that DOE is such an effective tool for protecting patents is that it compares inventions in fine detail. DOE examines how an invention works, not how it looks. This allows the court to see past superficial changes to see if infringement is present. 

While the concept may seem simple, applying it is often very complex. For example, both parties in a DOE case will often have an expert witness. This can confuse the fact of equivalency. Also, an element that is equivalent for one function may not apply to another function. This can make it very hard for a patent owner to prove their case. 

Another difficulty arises from how a patent is granted. Sometimes, a person applying for a patent may need to narrow their claims for approval. This narrowing prevents them from using broader claims in a DOE case. However, if the patent holder is a pioneer in their field, they will be able to argue much broader claims. 

There is also something known as the "reverse doctrine of equivalents." In a reverse DOE case, the defendant's invention may have been altered so much that it completes the same function but in a completely different way. If this is a case, it would be almost impossible for the patent holder to prove infringement. 

If you're considering a DOE case, it's a good idea to get advice from a patent attorney

Full Analysis

In many cases, there is no infringement found because there has been no full DOE analysis. This was the reason the EPOS Technologies Ltd. V. Pegasus Technologies, Ltd. case was overturned by the U.S. Court of Appeals. This case involved four patents. Summary judgment was granted to EPOS. Pegasus appealed the judgment. 

The Federal Circuit vacated the decision because the district court had not fully examined both products. The initial ruling was based on a superficial difference. It did not use the "function, way, result" test required for DOE claims. When a DOE claim is filed, the Court must perform a full analysis of both products in question. 

If a full analysis has not been performed, there is no way to determine equivalency. 

Another example of this is the Deere & Co. v. Bush Hog, LLC decision. This case involved rotary cutter decks. In the initial decision, the Court ruled that because the upper deck did not touch the lower deck in the Bush Hog cutter, it did not infringe on the Deere patent. However, this was overturned. The Federal Circuit stated the two decks engaged even though they did not touch, which infringed on the Deere design. 

In DOE cases, the results are what matters. Devices that perform the same function despite minor alterations infringe on patents

Frequently Asked Questions

  • When does the doctrine of equivalents apply?

The doctrine of equivalents applies when a when a patent holder proves that an invention is infringing on their patent by performing the same function.

  • What does "equivalent" mean?

An accused device is "equivalents" if it contains elements that are similar to elements in the patented device. They do not need to be identical. However, they do need to perform the same function.

  • Does design matter?

No. In a DOE case, design does not matter, only function. If two devices perform the same function in the same way with the same result, DOE applies and infringement has likely happened.

  • Are there defenses to DOE?

Yes. The most common defense is vitiation. This is when the defendant claims a jury could not reasonably identify equivalence. Vitiation does not mean there is merely an element missing, as a missing element may still have an equivalent.

  • Should I hire an attorney?

Certainly. DOE cases can get very complicated, and infringement can be hard to prove. An attorney can provide expert guidance in your case. They will be able to help you prove equivalence and can help you use hypothetical claims, if necessary. 

Get Help With Your Doctrine of Equivalents Claim

As you can see, doctrine of equivalents cases are extremely difficult. They require a large burden of proof and detailed knowledge. If you need help planning your doctrine of equivalents case, you need to get help from an experienced attorney like those you'll find on UpCounsel

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