Patents grant a limited monopoly to use an invention only insofar as the inventor's patent claims go. The patent applicant in her claims must carefully and specifically enumerate what the invention does that is novel and deserving of protection. Hence, products can be similar without violating patent laws, as long as the claims are substantially different or a non-patented product does not use any mechanism claimed in an existing patent.
Patents protect inventions (construed very broadly to include categories like plants and processes) and industrial designs. A patent holder has the exclusive right to use, manufacture or in any way reproduce, sell, promote or import an invention for 20 years, calculated from the filing date of the patent application. Patent holders also have the right to seek damages from those believed to be infringing on the patent and to license the patent to others.
Claims are the most essential part of a patent as they spell out in exact and technical detail what the patent covers. A patent can and usually does cover more than one claim for an invention, and there are different types of claims. Independent claims stand alone--the first claim in a patent is always independent (and usually the broadest claim)--whereas dependent claims only make sense in reference to a previous claim. A patent can have as many claims as the applicant deems necessary.
Industrial design claims are much simpler and consist only of a rendition of the design seeking protection (industrial designs have a shorter term of protection lasting 14 years from the filing date). However, U.S. Patent and Trademark Office officials have the authority to determine whether or not a design is too close to an already patented design, and such a decision can be somewhat subjective.
All patent applications in the U.S. undergo examinations, during which patent office officials determine if the invention is original and has not been previously disclosed, actually does what the claims state and does not infringe on any existing patents. Patent office officials have the authority to determine if an invention similar to one already patented violates any of the existing patent’s claims.
If the patent office decides that one or two claims in a patent application infringe on an existing patent, it will usually ask the applicant to remove those claims. However, if primary claims infringe on an existing patent, the application may be denied. The patent law office Brown & Michaels recommends talking to a patent attorney or agent before submitting an application if you are worried that your invention might infringe on an existing patent.