This paper initiates a structure for analysing problems involved in sequencing the operations that must be performed by a robot to tend machines in a cell. The sequence of operations is shown to be important in determining the feasibility of assigning a robot to tend machines and achieve specified production rates. Various cases, defined by the parameters that describe the system, are identified and analysed. Optimal sequencing procedures are described for several fundamental cases. Models are developed to prescribe solutions in more advanced cases, and the computational complexity of these cases is defined.