How do I know if someone is infringing my patent?
The most common type of infringement is direct infringement. For direct infringement, the patentee must show that the infringing party is either using, making, selling or offering to sell a product that infringes at least one of the claims of a patent either literally or under the doctrine of equivalents (DOE).
A product literally infringes when it exhibits all of the limitations of a claim. A wooden chair, for example, with four legs, a seating surface, and a seat back would literally infringe a patent that claims a wooden seating apparatus that includes at least four legs and a seating surface because the chair includes all of the limitations exactly as they are recited in the claim. A chair with three legs would not literally infringe because it does not include at least four legs and a metal chair would similarly not literally infringe because it is not wooden.
A product that does not literally infringe because it does not exhibit all of the limitations of a claim may nonetheless infringe under the DOE. Under the DOE the product exhibits an equivalent limitation in place of at least one of the claimed limitations. The patentee, however, cannot regain any subject matter that was disclaimed during prosecution. For instance, the three legged chair in the example above would not infringe under the DOE because three is not equivalent to four. The metal chair may infringe under the DOE if metal was used because metal has similar properties to wood. The metal chair would not infringe under the DOE if the metal limitation was added in an amendment to the claims during prosecution or if the applicant stated anywhere in the patent record that metal should not be used for the patented invention. For more information click here.