Nonlinear dynamic analysis and optimization of planar flexible multi-link mechanism with clearance considering the thermal deformation effect of kinematic pair

Traditional models of revolute clearance joint usually ignore the effect of bearing thermal deformation on the contact characteristics of kinematic pairs, leading inevitably to low prediction accuracy. In this work, a novel contact model of sliding bearing is first developed based on the thermal network method considering the thermal deformation effect of kinematic pair. The flexible connecting rod is discretized by non-shear locking deformation beam element and an improved dynamic model of planar flexible multi-link mechanism with clearance is further constructed. Compared to traditional rigid models, the simulation results based on the proposed dynamic model agree better with experiment values, verifying the validity of the model. Then, the effect of contact models, clearance sizes and crank speed on the nonlinear characteristics of multi-link mechanism is also analyzed in-depth using the established model. Results reveal that the existence of clearances can lead to chaos in the kinematic pairs of multi-link mechanisms and the viscous dissipation of lubricating oil is conducive to improving the system stability. Moreover, when the crank speed is lower than 180 rpm, the system is in a periodic or quasi-periodic state and then enter into a chaotic state as the crank speed increases. To improve the motion accuracy of slider and contact performance of revolute clearance joint, multi-objective optimization design of multi-link mechanism with clearance is finally further conducted using the proposed adaptive weight integrated learning particle swarm algorithm. It is demonstrated that the maximum penetration depth of the clearance joints after optimization is decreased, while the motion accuracy of the slider is significantly improved.