The PTO does a comparative study of every element of the claim to the product under acquisition. The PTO concludes that there is a literal infringement only if each element explained in the claim is present in the product under acquisition. For example, let us assume that the patent owner of a two wheeled motorcycle claims that a tri-wheeled automobile infringes his patent. Assume that the two wheeled motorcycle only consists of the following claimed parts being front and back wheels, the seat, the suspension holding the seat in position and the handle member. Now patent claims claiming each of these parts would have been written at the time of prosecution of the patent at the PTO.
In a literal infringement analyses, each of the claim elements are read and compared with the tri-wheeled automobile under acquisition. Here the PTO will read each element and conclude that although the tri-wheeled automobile has all features of two wheeled motorcycle but also has one extra wheel. Therefore this is clearly not a case of literal infringement. Then the PTO moves forward to check whether there is an infringement by the ‘doctrine of equivalents’. Under this method, although the claims do not interpret the accused products, if the product performs the same function in the same manner to provide the same result, then the product will be interpreted as an infringing product.
Doctrine of Equivalence:
When the claims of the product under acquisition and the patented product are interpreted by the PTO and if the PTO is unable to find literal infringement then the PTO checks for infringement by the doctrine of equivalence. This is a very subjective and also a highly debated process of patent law in the United States. This section simply describes the fundamentals of this doctrine and what it looks to accomplish.
The foremost investigation to decide whether there is infringement by doctrine of equivalence is to test for functioning of both products, process involved in the working of the products and the result obtained from both the products. This means that is the device under acquisition performs the same function in the same process to produce the same result, then it infringes under the doctrine of equivalence. On a later notice, various decisions have illustrated the “function/process/result” by stating that the difference between the product under acquisition and the patented invention should be non-substantial.
Now let us consider this in the light of the two wheeled motorcycle and tri-wheeled automobile example. Under this example, the tri-wheeled automobile performs the same function in the same process and produces the same result as that of the two wheeled motorcycle. Therefore although the tri-wheeled automobile does not literally infringe, it can be construed to infringe under the doctrine of equivalence.