| Power on/off and continuous operation are two important factors impacting the reliability of electronic and electro-mechanical components. In the reliability field, only limited work has been done to model component reliability involving transient phases and on/off cycling. This is due to difficulties in collecting data as well as establishing meaningful models which fit the data.; The purpose of this research was to study and model simple electro-mechanical components over a two-phase (on/off) life cycle under multiple stresses. In addition, this research was directed at determining a criterion for selecting between continuous and on/off operating policies.; A reliability experiment was designed to study the on/off switching effect and continuous operation effect, under multiple load and voltage stresses, for simple electro-mechanical dc motors. A real-time C program was used for control and to monitor the lifetimes of the dc motors.; A failure mode analysis was used to study the physical causes by which the motors failed. Based on the results obtained, it was concluded that only one mode (a brush/commutator) failure mode was present. Continuous operation provided a longer life than on/off operation under the same environmental conditions, when off-time was removed. A general reliability model, based on the two-parameter Weibull proportional hazards life distribution, was developed. Due to the proportional hazards (common Weibull shape) nature of the model, a set of acceleration factors were developed to relate the stress level. The calculated stress factor included multiple stresses.; Using this reliability model, different operating policies under different multiple stresses can be studied. The stress factor reliability model was extended to develop a simple policy decision rule. The rule compares the inverse of the stress factor with the demand duty cycle to determine the most effective operating policy. Hence, a quantitative analysis model, based on predicted reliability, has been developed to determine whether a continuous running policy or an on/off operation policy should be specified. |
