Narrow Results

Based on the elastic mechanics theory, the mathematical models of axial stiffness and torsion stiffness are constructed in accordance with single end thrust and two ends thrust. The effects of stiffness on dead band error are analyzed. With the analysis of displacement deviation induced by axial stiffness and angular displacement deflection caused by torsion stiffness, a formula to calculate the dead band error is presented. A model for Computer Numerical Control (CNC) machine tool feed system with stiffness is established. By applying computer simulation, dynamic performances, static performances and steady-state error of the system are analyzed. To reduce the effect of stiffness on the system, the feedforward control method is used to compensate stiffness. The simulation analysis shows the result that dynamic and static performances are improved, as well as steady-state error of the system is reduced by more than 58% with this approach.

In order to solve the problem that classical criticality analysis can't indicate randomness and fuzziness of mechanical failure, a new method of failure analysis is presented based on triangular fuzzy number. Considering influence of fault frequency, maintenance costs, maintenance time, fault effect, decision matrix is established with triangular fuzzy number. In order to reduce subjective influence of determining weights by experts directly, linear programming equations are established to obtain weights by Hausdorff distance. Finally, through establishing possibility degree matrix at different levels of risk attitude, criticality rank of each failure mode is obtained. Taking a case study of XK7132 CNC milling machines, the results show that bearing failure is the most hazardous failure mode. Compared with classical criticality analysis, method in this paper is more scientific and reasonable, and provides a theoretical basis for improving reliability of CNC milling machine.