In United States patent law under the patent act, a granted patent gives the patent owner the right to exclude others from making, using, selling, importing and exporting what is “distinctly claimed” in the patent. Although there is typically uncertainty regarding the proper interpretation of claimed limitations in a patent, the claims provide for public notice to gauge the limits of the patent owner’s rights upon a patent being granted.
If another is performing a right granted to a patent owner they are infringing the patent. Patent infringement generally falls into two different categories, literal infringement and infringement under the doctrine of equivalents.
The term literal infringement means that each and every claimed limitation has an identical correspondence to the alleged infringing device. However, if the accused device does not literally infringe a claimed limitation in a patent, the device may still infringement under the doctrine of equivalents. The doctrine of equivalents extends a patent owner’s rights beyond literal infringement, where a claim may be infringed upon if the difference between a claimed limitation and an accused device is “insubstantial.” To determine if a difference is insubstantial a three part test is used:
1. It performs substantially the same function,
2. In substantially the same way, and
3. To yield substantially the same result.
In applying this three part test, each claim limitation (not a claim as a whole) is compared with the accused device to determine if there is a substantial equivalent.
There are 4 main limitations to the doctrine of equivalents, being:
1. All elements ruled, (all of the elements of a patent claim must be present in an accused device)
2. Doctrine of public dedication, (a patent owner is precluded from asserting the doctrine of equivalents to cover unclaimed embodiments that are disclosed in the specification)
3. Existence of prior art, (the existence of an element in the prior art precludes the patent owner from asserting a scope of equivalence to encompass the corresponding element in the accused device) and
4. Prosecution history estoppel (narrowing amendments and arguments narrow the scope of the claimed limitation).
There are several things that patent attorneys need to be cognoscente about when dealing with the doctrine of equivalents in a patent law case.
First, the all elements rule requires that an accused device must contain at least an equivalent for each limitation. Yet, it can be difficult to determine exactly what a claim limitation is because when constructing claims, each individual word will be analyzed. Therefore, when drafting claims short claim sentences should be used to clarify exactly what the meets and bounds. Furthermore, it is important to use indentations to distinguish claim limitations from each other.
Second, the doctrine of equivalents is determined based on an issue of fact that must be adjudicated by a fact finder, such as a jury where the instructions to the jury are likely to be guided under the Federal Circuit Bar Association Model Patent Jury instructions section 8.4. However, the jury instructions in the Model Patent Jury instructions are slightly different than the three part test listed above.
Third, ranges outside of what ranges are claimed in a patent claim may be held to may be found to infringe based on the doctrine of equivalents. I feel like this is important to know as a last straw grasp to accuse infringement.
Fourth, the doctrine of equivalents is applied at the time of infringement and not at the time the patent was issued. As such, later developed technology may serve as an equivalent to a limitation in question. This portion of the doctrine of equivalents is important in fields such as mobile applications and computing software due to the rapid changes in technology and standards used. As such, if a patent is granted with claims directed towards location systems based on WiFi or GPS and new and improved location based systems are created, these types of systems may still infringe prior granted patents.