In a no-wait robotic flow-shop, the parts are transferred from a machine to another one by a robot and the time a part can remain on a machine is fixed. The objective is to maximize the throughput rate of the cell, i.e. to find optimal cyclic robot moves. In this paper, we consider identical parts in the balanced case (all processing times are equal). We present a conjecture which gives the structure of the optimal production cycle and prove it for several cases. These results confirm Agnetis conjecture which claims that, in a no-wait robotic cell, the degree of the dominant cycles can be bounded by the number of machines minus one (which simplifies the search of an optimal production cycle).