On/off cycling under multiple stresses

The authors describe an experiment, a model, and an analytic method for on/off vs. continuous policy evaluation. The methodology was developed and verified through experimentation. An experimental life-test of small DC motors was designed and performed; it involved on/off cycling vs. continuous operation under multiple stresses. A stress-factor reliability model based on the two-parameter Weibull proportional-hazards life distribution was fitted to the data. The analysis provides an estimate of the model parameters for the life distribution of the DC motors under two operating policies, while under multiple stresses. The characteristic life was related to the explanatory covariates: voltage, on/off cycling, and load. Due to the proportional hazards (common Weibull shape) nature of the model, acceleration factors were calculated to relate the stress levels. The reliability model was extended to develop a simple rule to aid in a decision between on/off cycling and continuous-run policies (to achieve higher reliability). The proposed model (with covariates) allows a much broader approach to reliability modeling than the usual Weibull model (without covariates) because it predicts the reliability under various environmental combinations