What's the difference between buying a patent and royalties ~ ~ ~ Do I have to pay royalties every time?

Purchase of patent: it belongs to patent transfer. After the transfer, the patentee belongs to the transferee. After the patent transfer fee is paid in one lump sum, the control right of the patent belongs to the transferee and has nothing to do with the transferor.

Patent royalty: it belongs to patent license, and the time limit and fee for the patentee to license users are the result of negotiation between the two parties. For example, during a certain license period, what is the license fee and how many times to pay it off.

I don't know if you understand.