Answered on Mar 08th, 2011 at 12:26 PM
There are two issues here. One is whether it is possible to obtain a new patent that builds on features of an old patent. Another is whether obtaining a new patent necessarily means that you have a right to manufacture.
The answer to the first question is yes, it is possible to obtain a new patent that builds on an old patented idea. In fact, many inventions build on old ideas.
The answer to the second question is no, just because it may be possible to obtain a new patent on an improvement of an old idea does not mean that you are not infringing someone else's patent. To be sure that you do not infringe on someone else's patent, you should hire an attorney to prepare an opinion on whether or not your new product infringes the old patent. Patent protection is defined by the claims section of the claims and the old patent may not cover exactly what you think it covers. It may also be possible to design around the old patent.