Research On The Design Method And Key Technology Of Functional Safety CNC System

Numerical control system plays an important role in the national economy, which determines the manufacturing capability of a country. With the continuous development of technology and our lives, high speed, high precision, intelligent and networked have become the trends of the manufacture system. As the brain of machine tool, CNC system is becoming much more powerful and complex than before. Therefore, functional safety of CNC system is also becoming important in order to guarantee the safe operation of the manufacturing process. However, there is no mature experience in the design of functional safety CNC system. Most of the functional safety control system in the world is focus on PLC and other process control system. How to guarantee the complex function and functional safety requirements of CNC system is the key problem of this thesis.The above problem is studied from hardware and software platform. Through the requirement analysis of functional safety CNC, the design method is laid down. In hardware aspects, firstly, functional safety assessment need to be done on standard hardware. Then with the result of functional safety assessment, hardware design would be improved in order to fulfill functional safety requirements. In software aspect, the software structure based on components will be employed. However, the functional safety software based on components is large, and its design process is complex. Therefore, a safety components sharing mechanism need to be researched to fulfill the rapid development of functional CNC system.The functional safety assessment method for the hardware of CNC system is studied first. The small sampled prior data of the hardware of CNC system is established based on the failure data of specified CNC system sampled in factory. Then failure probability distribution fitting of the hardware failure data is carried out. Quantitative analysis results shows that hardware failure probability distribution of CNC system meets the exponential distribution model. So that the mathematical model for safety assessment is laid down.For CNC hardware, the failure model based on fault tree and Markov functional safety analysis method is studied and designed. CNC system hardware has characteristics of big components number and complex structure. So CNC system hardware is divided into subsystems with Markov and fault tree analysis methods. Then fault tree analysis method is adopted to model and analyze the subsystems. The overall system analysis is then carried out using Markov model. In the constructing of the analysis model, entropy is used as criterion to calculate failure probability of subsystems. So the information weight can be distingue ished in the overall system. Therefore, the safety failure weights influence problem of every subsystem to the overall system can be well solved in CNC system.With the designed analysis model, Probability of dangerous Failure on Demand (PFD), Probability of Failures per Hour (PFH), Average Probability of average Frequency of dangerous failure (PFDavg), Diagnostic Coverage (DC) and Safe Failure Fraction (SFF) of system extended control unit, kernel processing unit, display unit and power supply unit of CNC hardware are calculated with fault tree and Markov method. IEC 62061 and IEC 61508 are employed to functional safety integrity level assessment. With the result, the design improvement discipline is made. Measures of redundancy design, error-detector circuit and derating design are proposed to improve the hardware of CNC system. With these measures, the desired functional safety performance is achieved.Software model of CNC is established according to IEC61131-3, IEC61131-6, IEC61508-3 and IEC61508-7, and implementation strategy of the software platform of CNC is also developed as well. In this strategy, a safety component sharing mechanism is established in order to solve the problem of the shortage of commercial safety components meeting IEC standards. Based on the research of the safety components knowledge representing, the safety components sharing platform is developed, and the design method of safety components knowledge base is also proposed. So that developers are able to develop the system and share resource conveniently. In the process of building knowledge base, safety components are represented with OWL. Then query and storage locating can be afforded for safety components through their description file. Ontology-based description has the reasoning ability. It can deal with the maintenance and query task of safety component knowledge base. Therefore, it provides a basis of massive cloud storage and application of the safety component knowledge in the future.In functional safety testing aspects of CNC system, implementation methods of networked functional safety CNC system is introduced firstly, and the possible reasons of failures are also analyzed as well. Then the testing methods of functional safety CNC system are introduced. Also, response time of different types of safety related systems is analyzed and compared. At last, a data sampling card for the testing of functional safety CNC system is developed, its technical principle and mechanism are introduced in detail. A functional safety CNC system testing platform is then developed based on the data sampling card, and functional testing and fault insertion testing are carried out. This testing platform gives a feasible reference for the functional safety testing of CNC system.CNC hardware safety assessment and design improvement, software design, testing platform are studied in this thesis. The research results provide a guidance for the design of functional safety CNC system. It provides a feasible solution for the design and implementation of functional safety CNC system with complex NC functions.