The hardware open structure of the CNC system is shown in the following aspects: a. The basic units that make up the system are all industrial-level modules. The hardware interfaces between them are in line with international standards, and have good compatibility and interchangeability. The addition, subtraction and replacement of modules does not involve other parts of the system; b. IPC and PC are fully compatible, enabling IPC-based CNC systems to take full advantage of the highly open resources of PCs. The so-called openness of CNC systems is based on the openness of PCs. The internal variables, input and output variables of the c.PLC are all open to the serial port and the user. The logical relationship between the variables can be independently programmed online according to different needs. In order to ensure the openness of the control system, the CNC system software with open structure divides the whole control program into two layers: the kernel layer is based on the real-time control software module of the basic hardware unit, the internal control hardware, the external output and the acceptance data, the module They are independent of each other; the shell layer is the link that connects the various modules of the kernel layer, and the work tasks of the hardware unit are allocated and dispatched by them. The information data between the inner and outer layers is transmitted through the following system common array variables: the feed increment L of the track in T; the absolute coordinate counter N of the grinding wheel center position; the backlash constant J of the table screw nut; the PLC input relay switch quantity X ; PLC output relay switch quantity Y; PLC auxiliary output relay switch quantity M; keyboard operation panel switch quantity K; file name array F of curve track file. The above L, N, J are 32-bit long integer arrays; F is an array of strings; X, Y, M, and K are Boolean arrays.
The shell layer shell layer, that is, the main program only involves tasks with low real-time requirements, and is mainly composed of the following two modules: CRT display module. Its main function is to dynamically display the current state of each common array unit in the form of graphics and text on the CRT, that is, the simulation LED counter and the workpiece animation correspond to N, the simulated various color indicators correspond to X and Y, and the simulated operation panel buttons Corresponds to K and so on. Analyze the command scheduling task module. Its main function is to scan the keyboard operation commands represented by each unit of the array K, to assign or cancel the task according to the value of K(i), to assign the relevant array to a given non-zero value when assigning the task, and to make the relevant array Zero value. The kernel layer kernel layer is composed of hardware-initiated interrupt service subroutines independent of the main program. There are three main modules: interpolator output module. The position controller is interrupted every T application. PLC communication module. X and Y are read-only memories, M is write-only memory relative to the CPU; X and M are read-only memories, and Y is write-only memory relative to the PLC; therefore, the specific task of the communication interrupt program is the input in the PLC, The output switch quantity is copied to the X and Y arrays in the CPU, and the M array value in the CPU is copied to the auxiliary relay in the PLC, that is, the X, Y and M arrays are dynamically refreshed at regular intervals. Keyboard command module. The task of this module is to dynamically map the switch state of the keyboard to the K array to form executable commands. The difference between the first two modules is that the interrupt is not timed, but is triggered by a change in the state of the keyboard keys. Redefining the PC keyboard works in sensor mode. Once an interrupt occurs, the service program converts the corresponding switch state to the corresponding K(i) value according to the previous definition. The value of K(i) is divided into two types according to definitions: follower and trigger.
The real-time guarantee of the CNC system, the system's working cycle cycle Once the hardware of the system is determined, the real-time nature of the control process is guaranteed by the execution of hardware interrupts. The duty cycle of the entire system is T. In order to ensure real-time performance, in an ideal situation, the CNC system is required to perform the following tasks in T: perform one interpolation and output sub-programs of pi and ni, set the required time to T1; execute a PLC communication program, refresh X, Y And M, set the required time to T2; execute a keyboard communication program, refresh K, set the required time to T3; the main program analyzes the command, schedules the task once, refreshes the CRT display once, and sets the required time to T4. Obviously, the real-time requirements of the system should meet T1+T2+T3+T4 (Finish)
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