Doctrine of Equivalents and Doctrine of Colorable Variation :

Patent infringement generally falls into two categories: literal infringement and infringement under the doctrine of equivalents. The term “literal infringement” means that each and every element recited in a claim has identical correspondence in the allegedly infringing device or process.

However, even if there is no literal infringement, a claim may be infringed under the doctrine of equivalents if some other element of the accused device or process performs substantially the same function, in substantially the same way, to achieve substantially the same result. The doctrine of equivalents is a legal rule in most of the world’s patent systems that allows a Court to hold a party liable for patent infringement even though the infringing device or process does not fall within the literal scope of a patent claim, but nevertheless is equivalent to the claimed invention.

This “expansion” of claim coverage permitted by the doctrine of equivalents, however, is not unbounded. Instead, the scope of coverage which is afforded the patent owner is limited by (i) the doctrine of “prosecution history estoppel” and (ii) the prior art.

An infringement analysis determines whether a claim in a patent literally “reads on” an accused infringer’s device or process, or covers the allegedly infringing device under the doctrine of equivalents. The steps in the analysis are:

• Construe the scope of the “literal” language of the claims.

• Compare the claims, as properly construed, with the accused device or process, to determine whether there is literal infringement.

• If there is no literal infringement, construe the scope of the claims under the doctrine of equivalents.

The doctrine of equivalents is an equitable doctrine which effectively expands the scope of the claims beyond their literal language to the true scope of the inventor’s contribution to the art. However, there are limits on the scope of equivalents to which the patent owner is entitled.

Doctrine of Colorable Variation: A colourable variation or immaterial variation amounting to infringement is where an infringer makes slight modification in the process or product but in fact takes in substance the essential features of the patentee’s invention.

In Lektophone Corporation v. The Rola Company, 282 U.S. 168 (1930), a patent holder’s patents were of sound-reproducing instruments for phonographs. According to the patent application, size and dimensions of the invention were the essence of the patent. The patent holder claimed that a radio loud speaker manufactured by the defendant (manufacturer) infringed the patents. The manufacturer’s devise also had a central paper cone, but the cone was smaller than that of the patented devise and that constituted colorable alteration. The court held that because colorable alterations of the manufacturer’s devise, it would not accomplish the object specified in the patent claims and hence did not infringe upon the patent holder’s claims.