1 In the introduction, the convex elliptical surface is the most widely used non-circular surface, and it is also a feature of the piston part. When turning, the cutter is required to move in the axial direction and can perform high frequency vibration in the radial direction to process the elliptical cross section. And convex curve. Non-circular cross-section parts (such as pistons for internal combustion engines) have ring grooves, conical surfaces, chamfers, etc. in addition to the convex-convex elliptic surface. Some aluminum pistons also have iron rings embedded in them. In actual production, in order to improve the efficiency and processing accuracy, it is required that the machining of all the profiles can be completed in one pass. General general-purpose CNC systems cannot meet the requirements for turning non-circular cross-section parts. It is necessary to organically combine general-purpose numerical control functions with non-circular cross-section machining. The current non-circular cross-section turning CNC systems all have a special CNC system structure. Parts are produced by a certain company in batches. Its internal structure is a “black box†for users or third parties, and there is a systematic selling price. The maintenance costs are relatively high and the shortcomings of general general purpose CNC functions cannot be achieved. We used the industrial computer as the hardware platform of the non-circular cross-section numerical control system to develop a user-oriented open CNC system with non-circular cross-section processing. The system unifies the special NC and non-circular section turning CNC and general CNC. Apart from the function of automatic turning non-circular section, it also has general CNC functions, such as: MST function, I/O function, fast forward retreat, straight line Circular interpolation and so on. 2 Non-circular cross-section turning open architecture 
Figure 1 linear servo unit block diagram
Figure 2 Characteristics of open non-circular cross-section numerical control system
Non-circular section turning special CNC function module to complete the non-circular section automatic turning servo unit is a closed-loop system with linear motor as the implementing agency, its structure is shown in Figure 1. The linear motor is a high-frequency, large-stroke, precision micro-feed device specially designed for processing non-circular cross-sections, and is also a drive mechanism of a tool. Its maximum stroke is 2mm and its maximum cutting force can reach 300N. Its linear servo unit can independently complete the closed-loop control of the linear motor and communicate with the outside world through the serial port. The non-circular section turning function module uses a grating sensor and a DSP signal processor, which can greatly improve the system's control accuracy and stability. Open-architecture features of non-circular section turning Open-type non-circular cross-section numerical control system features based on the IPC hardware platform are shown in Figure 2. The design idea of ​​the system is as follows: (1) Turning the non-circular cross-section special numerical control module, that is, the linear servo unit as the core, derives the host (IPC) upwards, and communicates with each other through the serial port. 2 With the IPC as the main control module, various general CNC functions are derived downward. Each function module communicates with the host through the computer bus. 3 Each numerical control function module is relatively independent, and the interface with the host is open, but its internal structure can be closed. The essential difference between the system and the special non-circular cross-section numerical control system is that the interface of each numerical control module is open to the user, and its peripheral functions adopt the form of plug-in. This kind of system structure does not depend on the specific structure of the subsystem, as long as the The address and interrupt vector are reserved in the host to meet the communication requirements between the host and each unit. That is, the internal structure of the linear servo unit may be a "black box" for a user or a third party. The open non-circular cross-section numerical control system has the following characteristics: 1 The general-purpose numerical control function module can use the inexpensive PC-based function card, which not only reduces the system cost, facilitates the user or the third party maintenance, but also enables the researcher to concentrate on the strength. Non-circular cross-section special CNC research: 2 can easily change the specific configuration of the system according to the needs of users, to meet the user-oriented design requirements. The so-called user-oriented, is to allow users to participate in the design of the system, and can own (or third-party) for maintenance. In the open non-circular cross-section numerical control system, all the numerical control function modules are based on the IPC hardware platform, and the interface between each module and the host computer is open, so it can turn special non-circular cross-section parts according to the needs of users. The numerical control function derives a variety of general-purpose numerical control functions, such as: MST, linear interpolation, circular interpolation, I/O functions, and the like. If a functional module fails during use, the user (or a third party) can replace the module alone without affecting the rest of the system. 3 The implementation of open non-circular cross-section numerical control system takes the IPC hardware as the platform, and derives a variety of general-purpose CNC functions based on the medium-convex variable ellipse NC cutting module to achieve chamfer, cone (face), end face and cut. Slots and other functions, the structure shown in Figure 3. The non-circular cross-section numerical control system in the figure is composed of a main control module, a linear servo unit, a spindle control unit, a position servo unit, and an on-site measurement system. The main control module is based on the industrial control computer, including hard disks, floppy drives, keyboards, monitors, and printers. It is the core part of the entire CNC system and is responsible for system management and information processing functions. In addition to communicating with each sub-function module, it also directly controls the system's I/O function. The information path of the industrial control computer and each function module can be divided into seven: 1 The microcomputer controls the linear motor through the interface circuit and the sub-CPU to realize the machining of the convex-convex elliptic surface: 2 The microcomputer controls the position servo through the dedicated control card to realize the interpolation. General CNC functions such as fast rewind and fast rewind: 3 Microcomputer control of spindle start/stop, rotation speed and tool holder through the interface circuit, inverter or tool holder box. 4 spindles pass the angular position information to the microcomputer through the encoder and interface circuit. :5 Microcomputer through the I/O board, optocoupler control buttons, display lamps and other input and output: 6 microcomputer through A / D conversion, micrometer to perform in-position detection of the finished workpiece, and display the measurement results: 7 alarm Channels, inverters, oil circuits, and hydraulic pressures are transmitted to computers through intermediate relays and interface circuits.
Figure 3 Overall system structure
4 Conclusion This CNC system combines non-circular cross-section processing special-purpose numerical control system with general general-purpose numerical control system. Not only can it realize the special function of non-circular cross-section processing, but also can realize other features of non-circular parts (such as ring groove, chamfer, etc.). ) and other auxiliary processing can greatly increase production efficiency. In addition, the numerical control software developed by this system greatly improves the reliability of the system and can realize the organic combination of dedicated and general-purpose numerical control functions. The use of DSP and gratings to achieve linear servo unit control, non-circular cross-section processing accuracy and system stability has also greatly improved. The system is currently used on a new generation of digital control piston lathes.
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