A quick summary of the process to determine whether your issued patent is being infringed by another.
1
Is your patent issued and maintained?
To allege infringement of a patent the patent must be: (1) issued by the PTO; and (2) be up to date on payment of maintenance fees.
2
What is the coverage of your Claims?
The Claims of a patent come at the end of the patent document. They define what you are protecting as your invention. The scope of the claims is determined: FIRST, by the claim language itself; SECOND, by the claim language with reference to the rest of the patent document; THIRD, with reference to any statements made while trying to get the patent application allowed (prosecution history); and FOURTH, by common definitions or understandings.
3
Isolate the elements of your patent claims.
Identify what are the elements of each claim in your patent.
4
Compare
Compare the allegedly infringing product/process/etc. with the elements of your claims. If you can find all the elements of your claim, then you may have a case for infringement. If one element is missing, then go to the next step.
5
Doctrine of Equivalents
If one of the elements is missing from above, then the missing element is evaluated to see if the allegedly infringing product/process/etc. has something that performs substantially the same function to produce substantially the same result as the missing element. This may satisfy the Doctrine of Equivalents. (HINT: you will really impress your patent attorney if you mention that you think that your prosecution history may prevent you from expanding the scope of the doctrine of equivalents argument.
Comments - add comment