2.2 System hardware structure
The hardware structure of the modified CNC system is shown in Figure 1. It consists of three parts: computer numerical control unit, servo drive unit (including motor) and measuring unit.
The numerical control unit includes an industrial PC, a position control module, an input and output module, and is the most basic unit that constitutes a numerical control system. The industrial PC can be configured with CPU, memory, display card, display, hard disk or electronic disk, floppy disk drive, etc. as needed; the position control module has multiple position detection interfaces, and collects the pulse signal of the photoelectric encoder as the position feedback of each coordinate of the machine tool. And control the speed unit through multi-channel D/A output signal, which can be matched with the all-digital AC servo unit and motor produced by Wuhan Huazhong CNC Co., Ltd., or with Siemens AG, AMK, Sanyo, and Matsushita of Germany. The drive unit is matched. The input and output module is the hardware input and output interface of the PLC embedded in the CNC system. The input and output voltage is 24V, and the maximum current is 100mA. It is used for the button signal input of the operation panel, the switch detection input of the machine tool, etc. The basic input/output points are 48/. 48 points can also be expanded to 256/196 points as needed.
The servo unit and motor are the most important guarantee for the reliable operation of the system. The AC servo unit uses a photoelectric encoder to achieve position detection feedback, 2500 pulses / r. The minimum resolution of the system is 0.001mm / 0.001 °.
The measuring unit is the necessary hardware component for the system to implement tool measurement and automatic tool setting. Includes signal processing modules and measuring components. The former mainly refers to A/D conversion and data filtering, the latter is tool measurement and tool setting sensor (probe), and contact or non-contact probe can be selected according to needs.
2.3 System Software Structure
2.3.1 Overall structure
The Huazhong I-type general-purpose CNC system is based on DOS development and adopts a layered modular structure. The system software is divided into four layers: the first layer is the operating system layer, including file management, process management, real-time task scheduling, and the physical management layer of the parameter database. The system management software is expanded on the basis of DOS, adding real-time task scheduling, CRT driver, and parameter library interface software. The entry to the task control is INT62, soft interrupt, with control primitives for scheduling, creating, suspending, undoing, blocking, waking up, delaying, and getting the status of the task. The second layer is the input and output layer of the machine tool, including position loop control software, MST code output, adjustment management and digital input and output. The position control software receives control and position commands through the internal communication area and passes the position control commands to the servo unit. The third layer is the interpolation control layer, which is interpolated by ISO code, including interpolation, tool compensation and program compilation. The fourth layer is the user operation layer. The specific content of each layer is shown in Figure 2. This hierarchical modular structure is easy to improve and transplant. Tool NC grinding automatic programming software and tool measurement and automatic tool setting software are integrated in the user operation layer.
2.3.2 Tool CNC grinding automatic programming software [2]
The structure of the tool NC grinding automatic programming software is shown in Figure 3. The software is mainly composed of the following parts:
(1) The process database programming software collects the relevant process data of the tool to be programmed, organizes and manages it with a suitable data structure, and forms a process database. These process data include numerical control system information, machine structure information, tool geometry parameters, grinding wheel shape parameters, machining process information, and machining process parameters. The process database is the support of the entire programming software. The numerical control system information is the information describing the numerical control code format of the numerical control system used, and is the information necessary for the format conversion in the post processing; the machine structure information is used to describe the structural model and structural parameters of the numerical control tool grinding machine, including the machine tool model code, The initial positional relationship between the coordinate axes of the machine tool kinematic chain and the direction of the motion axes of the machine tool [2]; the tool geometry parameters refer to the structural parameters and cutting parameters of the tool being machined, and the tool structure elements are used as the basic objects; the shape parameters of the grinding wheel are The parameters used to describe the shape and size of the grinding wheel; the machining process information is used to describe the machining process of the programmed machining tool. The system classifies, organizes and grinds the grinding process of various tools with the basic components of the tool structure. Management, forming a processing operation library; processing technology parameters mainly refer to the feed speed, main cutting speed, feed amount, machining allowance, coolant switch and other information in the various processing steps of the tool.
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