Based on state space, a variation propagation model of multi-station assembly of precision mechanical system was developed. Machining errors generally have great effects on the performance of mechanical system, especially precision mechanical system. In a multi-station assembly process, machining errors at each station accumulate and propagate to other parts, which will eventually degrade assembly accuracy and performance of the system. The differential motion vector was adopted to represent machining errors by the state vector in the model. Considering form errors, an innovative concept of mating coordinate system was proposed. This mating coordinate system, defined by two mating surfaces, can reflect real mating conditions more accurately. Detailed derivation for variation propagation modeling was presented. Finally, state equation and observation equation that can be used to guide measurement were obtained. In conclusion, the model we established can guide fault diagnosis and process design evaluation of precision mechanical system.
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