Multiple patents may be necessary to protect one technological invention
It is fairly common for more than one patent to be granted to a patent applicant on the same technological development. These patents are often said to be in the same “patent family,” and typically include the same description and drawings and differ only in the wording of the patent claims. There are a number of reasons why multiple patents may be desirable to cover what appears to a layperson to be the same invention.
In some cases, the patent examiner may refuse to examine different types of patent claims in the same application, such as claims relating to the structure of a device and claims relating to a method of using the device. It is acceptable to file claims addressing these different aspects of an invention in the same patent application, but an examiner is not required to examine claims covering all of these aspects in a single application if the examiner believes this would place an undue time burden on him or her. If the patent applicant desires to have patent claims granted on these different aspects of the invention, then additional (but very similar) patent applications may have to be filed with each application having claims of one of the different claim types. The multiple applications may then result in multiple patents being issued.
In other cases, the patent applicant may have initially settled for a patent with narrower patent claims but then filed a follow-up patent application to continue to pursue broader patent claims which also may result in an additional patent grant. However, it is also common for the U.S. Patent and Trademark Office to require patents on the same development to expire at the same time in the future so that the term of patent protection cannot simply be extended by filing multiple applications.