Once a patent is issued, it is up to the owner to enforce it. If friendly negotiations fail, enforcement involves two basic steps:
Because enforcing a patent can be a long and expensive process, many patent infringement suits aren't filed. Instead, the patent owner often settles with the infringer. Frequently, infringers pay a reasonable license fee that allows them to continue using the invention.
What constitutes infringement of a patent?
To decide whether a person is violating a patent, it is necessary to carefully examine the patent's claims (most patents contain more than one of these terse statements of the scope of the invention) and compare the elements of each claim with the elements of the accused infringer's 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 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 invention in the patent 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:
What remedies are available for patent infringement?
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.
Undertaking a patent infringement action can be tricky, because it is possible for the alleged infringer to defend by proving to the court that the patent is really invalid (most often by showing that the Patent and Trademark Office (PTO) 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 is dismissed, leaving the patent owner in a worse position than before the lawsuit.
When does patent protection end?
Patent protection usually ends when the patent expires. For all utility patents filed before June 8, 1995, the patent term is 20 years from date of filing, or 17 years from date of issuance, whichever period is longer. For utility patents filed on or after June 8, 1995, the patent term is 20 years from the date of filing. For design patents, the period is 14 years from date of issuance. For plant patents, the period is 17 years from date of issuance.
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 PTO, 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, 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.
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