Can I Patent an Invention Based on Expired Patent?

Dear Rich: After going through many cycles in regard to creating a patent that is similar or could be viewed as an enhancement to a current product, I found the patents that had been issued for a similar product ended in 1989. Given that utility patents expire in 20 years, what prevents me from creating my patent and using anything I want from the expired patent? Or, what are the ramifications of taking an expired patent as the framework of a product? You're using the term patent in two ways -- to refer to your invention, and to refer to the government sanctioned monopoly granted for new inventions. The emphasis in the latter is on "new" (and not obvious to others in the field). Existing prior art -- basically, that's any stuff that existed before you created your invention (whether patented or not) -- can't be the subject of your patent because it's not "new."

Nothing new under the sun. The vast majority of famous inventions are improvements of some kind. The lightbulb improved upon existing technologies (as did almost all of Edison's inventions). Alexander Graham Bell's invention was filed as an "Improvement in Telegraphy" and George Westinghouse's famous patent was for an "Improvement in Steam-Power Brake Devices."

So, if you improve on an existing invention (or expired patent), you may be able to acquire a patent for your improvement, but not for the underlying prior art. This article and this article both explain the distinctions. So to the extent you can separate and identify the improvement, you may be able to acquire a patent on that.