Reconstruction of CNC system of the hottest CNC to

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NC system transformation of NC tool grinder

[Abstract] this paper puts forward the technical route and technical scheme of NC system transformation of imported or domestic old NC tool grinder by using the special NC system of Huazhong 2000 tool grinder, analyzes the functional structure of the NC system, and finally gives a specific transformation example

1 preface

CNC tool grinding machines, especially multi axis CNC tool grinding machines with multi axis linkage, are high-efficiency and high-quality key equipment for grinding and manufacturing precision and complex shape tools. They are also electromechanical high-tech products with complex structure, high degree of automation, high accuracy and reliability requirements in all kinds of CNC machine tools. Their research and development has considerable technical difficulties. Using CNC tool grinder to grind tools must rely on tool grinding technology and programming technology. At present, the grinding technology and programming software of various complex shape tools also belong to patented technology or confidential technology abroad. Because of this, at present, only a few manufacturers in the world can produce high-performance CNC tool grinders

in order to improve the level and quality of China's tool manufacturing process, some domestic tool manufacturers and application manufacturers have introduced CNC tool grinders from abroad. After a long time of use, these CNC machine tools have basically intact host performance and can still be used, while their CNC system has fallen far behind modern CNC system technology and belongs to obsolete products. Some domestic manufacturers have also developed CNC tool grinding machines, but because the host machine is self-made and the CNC system is imported, this CNC tool grinding machine product is not only costly, but also because the general CNC system does not integrate tool grinding technology and programming software, it is difficult to realize the grinding processing of tools (especially complex tools). Therefore, the CNC system of these domestic CNC tool grinders must also be transformed

the latest special CNC system of foreign CNC tool grinder manufacturers is usually used for the above-mentioned CNC system transformation. Although this transformation scheme has the advantages of mature technology, low risk and guaranteed reliability, it also has many defects, such as high price and poor pertinence of process programming. The special CNC system for Huazhong 2000 tool grinder is an integrated CNC system successfully developed for the grinding of various rotary tools on the basis of the scientific research achievements of the national "Eighth Five Year Plan" key research project "product development of CNC universal tool grinder". With this system, the above problems can be solved well and the cost is low

2 function and structure of the transformed CNC system

2.1 basic functions of the system

after the transformation of the tool grinder with Huazhong 2000 tool grinder CNC system, the system has the following three basic functions

the function system of the general NC system retains the basic functions of the original general NC system, such as the axis control function of 16 axis NC and 9 axis linkage at most, the program verification function, the MDI function, the interpolation function of straight line, arc and helix, the m, s and t functions, the fault diagnosis display function, the embedded PLC function, etc

automatic NC programming function the biggest feature of this system is that on the basis of the standard general NC system, the tool grinding programming software is integrated, and the structural dimension and processing technology of the grinded tool are directly input on the CNC system in the form of graphic menu, which can be automatically programmed and processed, realizing the integration of programming and processing

tool measurement and automatic tool setting function in this system, the tool measurement function is integrated into the NC system. In the NC grinding of cutting tools, automatic tool setting solves the problems of cumbersome manual tool setting and poor accuracy

2.2 system hardware structure

the hardware structure of the transformed CNC system is shown in Figure 1, which is mainly composed of three parts: computer numerical control unit, servo drive unit (including motor) and measurement unit

Figure 1 system hardware structure

CNC unit includes industrial PC, position control module, input and output module, which is the most basic unit of CNC system. The industrial PC can be configured with CPU, memory, display card, display, hard disk or electronic disk, floppy drive, etc. as required; The position control module has multiple position detection interfaces, which collect the pulse signal of the photoelectric encoder as the position feedback of each coordinate of the machine tool, and control the speed unit through multiple d/a output signals. It can not only be matched with the full digital AC servo unit and electric machine produced by Wuhan Huazhong CNC Company, but also with the driving units of Siemens, AMK, Sanyo and Panasonic. The input/output module is the hardware input/output interface of PLC embedded in the CNC system. The input/output voltage is 24V and the maximum current is 100mA. It is used for button signal input of the operation panel and switch detection input of the machine tool. The basic input/output points are 48/48 points, and can also be expanded to 256/196 points as needed

servo unit and motor are the most important guarantee for the reliable operation of the system. The AC servo unit adopts photoelectric encoder to realize position detection feedback, with 2500 pulses/r. The minimum resolution of the system is 0.001mm/0.001 °

measuring unit is a necessary hardware component for the system to realize the functions of tool measurement and automatic tool setting. It includes signal processing module and measuring element. The former mainly refers to a/d conversion and data filtering, while the latter refers to tool measurement and tool setting sensor (probe), which can choose contact or non-contact probe according to needs

2.3 system software structure

2.3.1 overall structure

central China type I General NC system is developed based on DOS and adopts hierarchical 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 physical management of 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 of task control is int62, soft interrupt, which has control primitives for scheduling, creating, suspending, revoking, blocking, waking, delaying and acquiring task status. The second layer is the input and output layer of the machine tool, including position loop control software, MST code output, coupling management and switching value input and output. The position control software receives the control and position command through the internal communication area, and transmits the position control command to the servo unit. The third layer is the interpolation control layer, which is ISO code interpolation, including interpolation, tool compensation and program compilation. The fourth layer is the user operation layer. The specific contents of each layer are shown in Figure 2. This hierarchical modular structure is convenient for improvement and transplantation. Tool NC grinding automatic programming software and tool measurement and automatic tool setting software are integrated in the user operation layer

Figure 2 system software structure

2.3.2 tool NC grinding automatic programming software [2]

the structure of 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, and adopts the appropriate data structure to organize and manage, forming the process database. These process data include CNC system information, machine tool structure information, tool geometric parameters, grinding wheel shape parameters, machining process information and machining process parameters. He helped design and produce many experimental data in this paper. Process database is the support of the whole programming software. NC system information is the information that describes the NC code format of the adopted NC system and is necessary for format conversion in post-processing; The machine tool structure information is used to describe the structural model and structural parameters of the CNC tool grinder, including the machine tool mechanism model code, the initial position relationship between the coordinate systems of the machine tool motion chain, and the direction of each motion axis of the machine tool [2]; Tool geometric parameters refer to the structural parameters and cutting parameters of the machined tool, which are described with the tool structural elements as the basic object; The shape parameters of grinding wheel are used to describe the shape and size of grinding wheel; The machining process information is used to describe the machining process of the programmed machining tools. The system takes the tool structure elements as the basic unit to classify, organize and manage the grinding processes of various tools, forming a machining process library; Processing parameters mainly refer to the feed speed, main cutting speed, feed rate, machining allowance, coolant switch and other information in each processing procedure of the tool

Figure 3 structure of automatic programming software for tool NC grinding

(2) parametric input module parametric input module is the interface of programming software to realize human-computer information interaction. The module calls out the relevant process parameters from the process database by inputting the processing information, and then makes necessary modifications to the process information according to the specific processing object, processing conditions and processing requirements, and generates data files for the subsequent tool position calculation and tool position verification module and post-processing module. Specifically: CNC system settings, machine tool settings, tool settings, process settings, grinding wheel settings, process settings

(3) programming library and tool position calculation and tool position verification module programming library is the package of tool position calculation program and tool position verification program of all programmed tools of programming software. The function of the tool position calculation and tool position verification module is to read out the machining element information, grinding wheel cutting surface information and process information of each machining process of the tool in sequence from the machining process file, and call the corresponding tool position calculation program and tool position verification from the programming library according to these information to generate the tool position data file and CC point data file. Tool position calculation and verification are the key of automatic programming, and the programming library is the core of the whole programming software

(4) post processing post processing is the process of converting the tool position file generated after tool position calculation into the NC code that can be executed by the NC tool grinder. It includes machine tool motion solution, nonlinear machining error verification and processing, feed speed verification and correction, file format conversion, etc

2.3.3 tool measurement and automatic tool setting software

the software includes two relatively independent software modules: tool measurement and automatic tool setting, which are based on a common hardware structure. The function of the tool setting software is to determine the relative position relationship between the programming coordinate system and the machine tool coordinate system. As long as the hardware is reliable, the software implementation is relatively simple

for tool regrinding, because the theoretical data about tool shape and cutting parameters are not known, the only basis for NC programming and processing is the tool physical model. The function of the tool measurement system is to convert the geometric analog quantity of the tool physical model into the geometric digital quantity that the automatic programming software can receive by sampling the tool physical model, so as to realize tool programming and processing. The tool measurement software is mainly composed of probe motion control module, data acquisition module and data processing module. The probe motion control module is the key of the whole software. For different tool types and processing requirements, different probe types, there are different motion control strategies (limited to space, this paper will not expand)

3 example of numerical control system transformation

as shown in Figure 4, a domestic aircraft manufacturer imported from Germany the heliconic 30 NC tool grinder produced by Walter company. The grinder has five machine tool motion axes (x, y, Z, a, b), which can realize the linkage of three axes (x, Z, a) numerical control two axes (x, a), and the other two axes (y, b) are manual axes. The tool grinder actually

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