N policy for redundant repairable system with additional repairmen

In this investigation, the reliability characteristics of a renewable machining system having M identical operating and S spare machines have been studied. The repair facility has an ordinary and r special repairmen who turn on according to the rule: (i) the ordinary repairman turns on (turns off) when there are N or more (none) failed machines; (ii) the ith (i=1, 2, …r) special repairman turns on (turns off) when there are N+im or more (less than N+im) failed machines in the system. A computational method is developed to derive reliability and mean time to failure (MTTF) and validated by taking an example. The cost analysis is done in order to obtain the optimal number of additional repairmen and spares based on the cost criterion subject to minimum reliability requirement. The effect of various parameters on system reliability is depicted by plotting reliability function. The MTTF has been compared for different sets of N and S and varying other parameters.