A patent owner may enforce his patent by bringing a patent infringement action (lawsuit) in federal court against anyone who uses his invention without permission. If the lawsuit is successful, the court will take one of two approaches. It may issue a court order (called an injunction) preventing the infringer from any further use or sale of the infringing device, and award damages to the patent owner. Or, the court may work with the parties to hammer out an agreement under which the infringing party will pay the patent owner royalties in exchange for permission to use the infringing device.
Bringing a patent infringement action can be tricky, because it is possible for the alleged infringer to defend herself by proving to the court that the patent is really invalid (most often by showing that the U.S. Patent and Trademark Office (USPTO) made a mistake in issuing the patent in the first place). In a substantial number of patent infringement cases, the patent is found invalid and the lawsuit dismissed, leaving the patent owner in a worse position than before the lawsuit.
Patent protection usually ends when the patent expires. Here are the expiration dates:
A patent may expire if its owner fails to pay required maintenance fees. Usually this occurs because attempts to commercially exploit the underlying invention have failed and the patent owner chooses to not throw good money after bad.
Patent protection ends if a patent is found to be invalid. This may happen if someone shows that the patent application was insufficient or that the applicant committed fraud on the U.S. Patent and Trademark Office (USPTO), usually by lying or failing to disclose the applicant's knowledge about prior art that would legally prevent issuance of the patent. A patent may also be invalidated if someone shows that the inventor engaged in illegal conduct when using the patent -- such as conspiring with a patent licensee to exclude other companies from competing with them.
Once a patent has expired or has been invalidated, the invention described by the patent falls into the public domain: it can be used by anyone without permission from the owner of the expired patent. The basic technologies underlying television and personal computers are good examples of valuable inventions that are no longer covered by in-force patents.
The fact that an invention is in the public domain does not mean that subsequent developments based on the original invention are also in the public domain. Rather, new inventions that improve public domain technology are constantly being conceived and patented. For example, televisions and personal computers that roll off today's assembly lines employ many recent inventions that are covered by in-force patents.
Although most inventors are concerned with the rights a patent grants during its monopoly, or in-force, period (from the date the patent issues until it expires), the law actually recognizes five "rights" periods in the life of an invention. These five periods are as follows:
For a clear guide to every step of the patenting process, read Nolo's Patents for Beginners, by David Pressman and Richard Stim (Nolo).
To decide whether an inventor is violating (infringing) a patent, it is necessary to carefully examine the patent's "claims." (Claims are terse statements of the scope of the invention, and most patents contain more than one of them.) The elements of each claim must be compared with the elements of the accused infringer's invention (usually a device or process).
If the elements of a patent claim match the elements of the device or process (called "reading on" or "teaching" the device or process), an infringement has occurred. Even if the claims don't literally match the elements of the infringing device, it is possible that a court would find an infringement by applying what's known as the "doctrine of equivalents"; that is, the patented invention and the allegedly infringing device or process are sufficiently equivalent in what they do and how they do it to warrant a finding of infringement.
For example, Steve invents a tennis racket with a score keeper embedded in the racket handle's end. The invention is claimed as a tennis racket handle that combines grasping and score-keeping functions. Steve receives a patent on this invention. Later, Megan invents and sells a tennis racket with a transparent handle that provides a more sophisticated score-keeping device than Steve's racket. Even though Megan's invention improves on Steve's invention in certain respects, it will most likely be held to be an infringement of Steve's invention, for one of two reasons:
In 2002, the Supreme Court handed down a ruling ( Festo Corp. v. Shoketsu Kinzoku Kabushiki Co. Ltd., 535 U.S. 722 (2002)) that makes it harder for patent owners who amended their patent claims to assert that others are infringing their patent. In essence, patent owners can use the doctrine of equivalents only if they can show that their amendment did not "surrender" the equivalents at issue -- a complex and confusing standard that requires the advice of a patent attorney.
In 2007, the Supreme Court modified the standard of nonobviousness applied in patent infringement cases for combination inventions and determined that "ordinary innovations" are not patentable (KSR v. Teleflex, 550 U.S. __ 2007).
If a case is brought to enforce a patent on a method or process invention, the defendant can escape liability if they were using the invention more than one year prior to the patent application date.