In the process of using the elastic pin coupling, we will find that the load transferred in the transmission shafting often changes, but the reasons for the change of the load are different, such as the motor speed is unstable, the load of the working machine is unstable and the dynamic load caused by the centrifugal force caused by the unbalanced rotating parts of the shafting may cause the change of the load. Load changes are often reflected in the periodic load, impact load and irregular change of load, and the coupling transmission can adapt to load fluctuations, with the ability of buffering and damping, mainly related to its stiffness and damping.

The stiffness of elastic pin coupling includes radial stiffness, axial stiffness and torsional stiffness. In practical engineering, load changes are often caused by torsional vibration due to torque fluctuations, so the main stiffness of coupling transmission is torsional stiffness. Generally, in the shafting drive, the stiffness of other parts of the system will be much larger than that of the elastic pin coupling. Therefore, in the simplified case, assuming that the elasticity of other parts is zero, only the elasticity of the coupling transmission parts is considered. The torsional rigidity of the coupling transmission is taken as the torsional rigidity of the transmission shafting.

Although the elastic pin coupling generally has the function of buffering and vibration absorption, but with a specified stiffness of the coupling transmission parts, not in every kind of variable torque can produce the effect of vibration reduction, sometimes it will cause stronger vibration. Therefore, only when the stiffness of the coupling fittings is coordinated with other parameters and loads of the entire transmission shafting, can the effect of vibration reduction be produced. In order to solve the kinematic differential equation of coupling accessories, it is necessary to simplify the mechanical models of moment of inertia and stiffness on the active and driven sides of coupling in the transmission shafting system.