What is the relation between Time Sharing operating systems and Round Robin CPU scheduler?
No.  A time-sharing computer switches between processes in some way or other.  A time-sharing computer with round-robin scheduling switches between processes in a particular way.  For instance, suppose there are three processes, A, B, and C.  A round-robin scheduler would switch between them in the order ABCABCABCABC etc.  Some other scheduler might switch between them in the order AABAABAACAABAABAAC (for instance).  Both are examples of time-sharing, but the latter is not a round-robin scheduler.

I suggest reading https://en.wikipedia.org/wiki/Scheduling_(computing).