Mechanical Modeling and Structural Optimization of Spindle System of Static Bias Point the Bit Rotary Steerable System

The fatigue life of the spindle system of the point the bit rotary steerable system largely determines its service life. At present, the mechanical modeling of the spindle system of the point the bit rotary steerable system generally simplifies the force of eccentric rings on the spindle to a known concentrated bias force, and fails to consider the constraint moment of eccentric rings to the spindle, which needs further optimization. Therefore, in this paper, the control and constraint conditions of the tool are considered, and a mechanical model of the biasing spindle with unknown binding force and constrained moment at the eccentric rings is established. On this basis, the geometric and mechanical equations of the spindle system are established, the expressions of deflection and rotation angle at each section of the spindle are derived, and the dimensions of the structure are taken as the known conditions to solve the unknown binding force and the constrained moment. In order to increase the service life of the spindle system, the optimization analysis of the structural dimension parameters involved in the model is carried out to reduce the binding force and constraint moment of the spindle system. According to the analysis results, the optimal value range of the distance ratio from eccentric rings to cantilever bearing and eccentric rings to ball bearing is 2–2.5.