Transmission compliance and hysteresis behaviors are associated with harmonic drives. The experimental observation of a harmonic drive showed that these behaviors are significantly degraded with increasing service time, and their accurate modeling is expected to improve the performance of the control system of harmonic drive-based devices such as robot manipulators. In this paper, a new model is proposed to capture transmission compliance and hysteresis and their degradation. The phenomenon is represented through a combination of the nonlinear stiffness component and the micro-sliding friction in the tooth engagement area. The proposed model considered the multi-tooth meshing and the interference effects of the reducer. The parameters of the model were identified using optimization techniques. Numerical simulations and experimental data using a specialized harmonic drive test device were compared to demonstrate the proposed model.

A tooth profile is of significant importance to the performance of a harmonic drive. Available studies about designing a tooth profile only consider the influence of the tooth profile on the meshing characteristics from a macro perspective. However, the effects of the surface roughness and contact geometry of the tooth on the lubrication characteristics from the micro perspective are rarely reported. In the present study, a double-circular-arc tooth profile is used as the basic tooth profile of the flexspline. Based on the modified kinematic method, a conjugate profile is calculated and the tooth profile of the circular spline is obtained. On this basis, the mathematical model for the mixed lubrication of the harmonic drive with a double-circular-arc tooth profile is established by considering the factors of the normal load of meshing point, relative velocity, contact geometry, and surface roughness. The comprehensive performance under different double-circular-arc tooth profile parameters (tooth face radius, tooth flank radius, and common inclination) is analyzed. To verify the correctness of the research, four sets of harmonic drives are designed and machined for testing their basic performance. The results show that the parameters of the double-circular-arc tooth profile have multiple influences on the comprehensive performance. The meshing performance and lubrication performance are restricted. Parameter control can effectively improve comprehensive performance and different tooth profile parameters should be designed for different applications.

The novelty of the present study is that it investigates the effect of propeller shaft deflection, caused by the propeller self-weight and interfacial mixed forces, on the fluid–solid–heat (FSH) coupling performance of water lubricated rubber stern bearing (WLRSB). In the FSH coupling model, the generalized average Reynolds equation and the Kogut–Etsion asperity contact model are used to determine the hydrodynamic and the elastic–plastic contact behaviors of WLRSB. In the thermal analysis, the journal, water film, and rubber bushing are considered as an integrated system (JWR system) using the Euler method. To prove the correctness of the developed model, the predicted results are verified by comparisons with the experimental results given in the literature. In addition, to assess the effect of the force-driven deflection during FSH simulation, comparisons of the FSH predictions between the aligned journal case and the deflected journal case are carried out. The results indicate that, especially under a heavy load condition, the deflection of the stern shaft should be incorporated into the lubrication gap between the journal–rubber interface during the analysis of FSH performance of the JWR system.