An industrial robot will service n production machines in a machine cluster. Each production machine is identical and has an automatic processing time Tm = 130 sec. The robot servicing and repositioning time for each machine is given by the equation (Ts + Tr) = 15 + 4n, where Ts is the servicing time (sec), Tr is the repositioning time (sec), and n = number of machines that the robot services. (Ts + Tr) increases with n because more time is needed to reposition the robot arm as n increases. The full cycle time for each machine in the cell is Tc = Ts + Tm.
(a) Determine the maximum number of machines in the cell such that machines are not kept waiting. For your answer,
(b) What is the machine cycle time, and
(c) What is the robot idle time expressed as a percent of the cycle time Tc?