Research And Implementation On Function Safety Of Hardware Platform Of Numerical Control Device

This study is under the “research of the numerical control system functional safety technology” subject to the national science and technology major project “High-end numerical control machine tools and basic manufacturing equipment”.It explored the quantitative evaluation method of the function safety level of domestic numerical control device, and carried on an “assessment-improvements-assessment” iterative design work. The main work includes the following steps: the determination of failure distribution model, the failure mode effect and diagnosis analysis, function safety assessment model-building and improvement of the hardware design.After the initial choice of normal failure distribution types,it draws the scatter diagram whose datas came from the field feedback. And the failure distribution is determined by the fitting degree between scatter diagram and the common failure distribution curve. FMEDA is the basis of computing hardware failure probability. It mainly contains the following two parts: source of failure data and failure mode. The source of failure data is obtained by using the mathematical statistics method from GJB/Z299, and the components failure modes are divided according to IEC62061. The failure parameters as well as PFH of each subsystem that affect the safety level is calculated by using the model of reliability diagram based on the fault tree and Markov which satisfied the failure distribution type. Then the safety integrity level SIL of the device can be dealt by the PFH value. At last improvement work is taken based on the safety assessment result especially on the four fields: purchase of components, limit reduction,diagnostic design and redundant configuration. After that, the safety integrity level of the improved system hardware platform has reached the expected target SIL2.By completing the works above, this study has completed the construction of numerical control device’s function safety assessment. It has a high feasibility and operability on the engineering applications. This laid a solid foundation for further implement of domestic safety numerical control products.