| Diesel engine is widely used in modern ships as power plant. Piston is the key component of the diesel engine, and how closely the piston combines with the cylinder directly affect the diesel engine performance. By improving the machining technology of the piston, the diesel engine power could be improved and the fuel consumption could be decreased. With the velocity and workload of diesel engine continuously increasing, the cross sections of ship piston are always designed as special shape, and non-circular middle-convex and varying oval (NMVO) surface contour is widely adopted as the profile of piston skirt. When traditional processing method is used for the NMVO piston, low efficiency and poor coherence of machining precision will arise because of the complicated shape and the high precision requirement, so non-circular numerical control turning is widely used to cut NMVO piston for high efficiency, high precision, flexibility and high economic benefit. Financially supported by the "Important&Specialized Science and Technology Project of Ministry of Industry and Information Technology of the People’s Republic of China"(2011ZX04002-132), a new derived CNC lathe system for ship piston turning is developed in this paper. The main work is summarized as following.1. By analyzing the shape features and processing principle of NMVO piston, a new control system scheme consisting of industrial computer and embedded real-time controller was proposed based on the research of the relationship between the real-time performance requirement of the NC system and the technical index of machine tool, and the technical index of this type of NC system is derived.2. By employing traditional lathe CNC as an independent intelligent module with high autonomy, a derived CNC lathe system was developed. The synchronization between lathe CNC and derived modules was realized based on the finite state machine model of the lathe CNC.3. The hardware and software of the derived controller were developed based on TMS320F28335DSP. By proposing a time-triggered hierarchical finite state machines (TTHFSM) pattern for embedded real-time software developing, the HFSM model of the derived controller software was built, and the driver program, function modules and synchronization control module were developed based on FSM pattern. The program developed based on this pattern could nicely meet the real-time request of the system, and the developing efficiency and reliability were improved.4. By combing the automatic code generation function of the Simulink and Real-Time Workshop in Matlab with a Lab VIEW based experiment data receiving software, a new servo control experiment system for VCM (Voice Coil Motor) was developed. The automatic programing and real-time monitoring at high control frequency were realized and the efficiency of VCM control algorithm developing and experiment was improved.5. A VCM motion controller was developed using modified discrete-time repetitive control and PI control. By using low-pass filter and stable filter the stability of the repetitive control system was improved, and the PI controller was employed to inhibit random disturbance. The tracking accuracy of the VCM met the project requirement by using this controller. 6. The validity and reliability of the derived CNC lathe were verified by system adjustment and practical processing experiment. |
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