Durability Calculation for Gear Mechanisms in Electromechanical Actuators

Electromechanical actuators for aircraft and space vehicles consist of cylindrical gears or combinations of various gear types including bevel and planetary gears at the preliminary stages and harmonic drives at the final stages. Gears at the preliminary stage differ from each other in transmission ratios, gear wheel sizes, materials, transmitted loads, rotational frequencies and other parameters. Life of gears affects their wear and at the same time can be used as an indicator of dynamic activity and crucial importance in relation to the factor that determines the possibilities of using high accuracy electromechanical actuators, for example, in rotation mechanisms of spacecraft antennas. The wear is often characterized by its intensity, which is understood as a ratio of the wear to the sliding distance where the process occurs. The intensity has an advantage over other wear characteristics because its numerical value does not depend on the choice of the system of units of the defining variables. Wear intensity can vary largely. It depends on the type of contact interaction between mating surfaces, materials, environment, nature of the mechanical and chemical processes in the contact area as well as on the stresses, sliding velocity and ambient temperature. When friction occurs in normal atmospheric conditions, oxyl and adsorbent films are formed on the contacting surfaces. They decrease the intensity of the wear by breaking when sliding, and therefore preventing material damage in the thin surface layer. The authors propose a method of calculating the durability of gears at the preliminary stage of electromechanical actuators with regard to the wear criterion. The method is supported by an experimental and theoretical study of wear intensity. The formulas obtained can be used for evaluating gear durability.

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