Degradation modeling and reliability estimation for mechanical transmission mechanism considering the clearance between kinematic pairs

The mechanical transmission mechanism is the core component of electromechanical systems, of which the health state can affect the accuracy and stability of the entire system. Due to machining errors and thermal deformation, clearance often exists between the kinematic pairs, which leads to irregular collision- separation during the operation. The clearance size and the surface quality of pairs change during the service life, leading to the time-varying damage and degradation state of the mechanism. Therefore, the kinematic pairs suffer from not only natural deterioration process such as wear, fatigue, etc., but also the collision-separation process caused by the clearance. In this paper, a degradation and shock model for the mechanical transmission mechanism is proposed considering the influence of clearance between the kinematic pairs. The degradation process is divided into running-in stage, stable degradation stage, and fast degradation stage according to the health states, and is modeled by a transformed gamma process to account for the dependency between service time and health state. Random shocks caused by the collision-separation process are classified into different zones in terms of their sizes, and the arrival rate of the shocks also change with the health state of the mechanism. The closed-form reliability function is derived and verified by the experiment of rotating pair of the crank and rocker mechanism. Results show that the proposed degradation and shock model can obtain a more realistic and reasonable reliability of the transmission mechanism.