Sue for patent infringement after the patent expires.

Although the patent law of the United States has not been studied, the basic principles of the law are the same. As far as the civil law system is concerned, the patentee has the right to investigate the tort liability of the infringer before the patent protection period. After the expiration of the patent protection period, the original patentee still has the right to investigate the tort liability before the expiration as long as it does not exceed the limitation of action prescribed by law.