1.2.1 Composition of CNC machine tools
A CNC machine tool is a machine tool that uses CNC technology to implement processing control. It is a typical product of mechatronics. It is an automation device that integrates machine tools, computers, motors and their driving, motion control, detection and other technologies. CNC machine tools are generally composed of input/output (1/O) devices, numerical control devices, servo systems, measurement feedback devices and machine tool bodies, as shown in Figure 1-5 and Figure 1-6. Table 1-3 shows the detailed introduction of each component of the CNC machine tool.
Figure 1-5 Composition diagram of CNC machine tool
Figure 1-6 Detailed block diagram of CNC machine tool composition
Table 1-3 Detailed introduction of each component of CNC machine tool
| Serial number | Content | Detailed description |
| 1 | input/output device | When the CNC machine tool is working, there is no need for people to directly operate the machine, but it is necessary to execute the intention of the person: this must establish a certain connection between the human and the CNC machine tool. The intermediate medium of this connection is the program carrier, which is often Known as the control medium, when processing parts on an ordinary machine tool, workers operate the machine tool for processing according to the drawings and process requirements. In CNC machining, the control medium is the information carrier that stores all the actions required for CNC machining and the position of the tool relative to the workpiece. It records the machining process of the parts.
In CNC machine tools, the commonly used control quality is perforated paper tape, cassette tape, floppy disk, U disk, network and other carriers that can store codes. As for which one is used, it depends on the type of CNC system. The 8-unit (8-hole) perforated sheet was used in the early days, and the standard information code ISO (International Organization for Standardization) and EIA (developed by the American Electronics Industry Association) two codes were specified. With the continuous development of technology, the quality control Also improving. Different control quality has corresponding input devices: punched paper tape, to be equipped with photoelectric reader; cassette tape, to be equipped with VCR; floppy disk, to be equipped with floppy disk drive and drive card. Modern CNC machine tools can also input programs through manual mode (MDI mode), DNC network communication, R-232C serial communication or even direct U disk copying. |
| CNC device | Numerical control device is the core of numerical control machine tool. It receives the processing information in the NC program input by the input device, and sends corresponding instructions to the he server system after decoding, calculation and logic processing. The servo system drives all moving parts of the machine tool to act according to the predetermined requirements of the NC program. The numerical control device is a special computer composed of central processing unit (CPU), memory, bus and corresponding software. The function of the whole numerical control machine tool is mainly determined by this part. As the “command system” of the numerical control machine tool, the numerical control device can complete the input of information Storage, transformation, interpolation and various control functions. Its main functions are as follows: ① Multi axis linkage control ② Interpolation of various functions such as line, arc and parabola ③ Functions of inputting, editing and modifying NC programs ④ The conversion function of NC machining information, including iso/eia code conversion, metric English system conversion, coordinate conversion, absolute value and relative value conversion, counting system conversion, etc ⑤ Tool radius and length compensation, transmission gap compensation, pitch error compensation and other compensation functions ⑥ With fixed cycle, repeated processing, mirror processing and other processing methods ⑦ Display characters, tracks, graphics, dynamic presentation and other functions on CRT ⑧ With fault self diagnosis function ⑨ Communication and networking functions |
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| 3 | Servo system | The servo system is composed of a servo drive motor and a servo drive device, and is a drive component that receives the instructions from the numerical control device to drive the machine tool actuator to move. It includes spindle drive unit (mainly speed control), feed drive unit (mainly speed control and position control), spindle motor and feed motor, etc. Generally speaking, the servo drive system of CNC machine tools requires good fast response performance and functions that can track commands sensitively and accurately. The servo systems of CNC machine tools include stepper motor servo systems, DC servo systems and AC servo systems. Now the latter two are commonly used, both with position detection components such as induction synchronizers and encoders, while AC servo systems are replacing DC. The executive parts and mechanical transmission parts on the servo system machine tool constitute the feed system of the CNC machine tool, which controls the feed speed, direction and displacement of the executive parts according to the speed and displacement commands sent by the CNC device. Each execution part of the feed movement is equipped with a set of servo system. The function of the servo system is to convert the pulse signal from the numerical control device into the movement of the moving parts of the machine tool. Process parts that meet the requirements of the drawings |
| 4 | Feedback device | The feedback device is the detection link of the closed-loop (semi-closed-loop) CNC machine tool, which is composed of detection elements and corresponding circuits. Its function is to detect the actual moving speed and displacement of the coordinate axis of the CNC machine tool, and feed back the information to the CNC device or the servo drive device to form a closed-loop control system. The installation of the detection device and the position of the detection signal feedback depend on the structure of the numerical control system. A system without a measurement feedback device is called an open loop system. Because the advanced servo system adopts the digital servo drive technology (called digital servo), the bus is generally used to connect the servo drive device and the numerical control device. In most occasions, the feedback signal is connected with the servo drive device and transmitted to the numerical control device through the bus. Only in a few occasions or when an analog control servo drive device (called an analog servo device) is used, the feedback device needs to be Connect directly to the numerical control device. The built-in pulse encoder, induction synchronizer, grating and magnetic ruler in the servo motor are all commonly used detection devices for CNC machine tools. Servo system and detection feedback device are the key links of CNC machine tools. |
| 5 | Machine body | The body of the machine tool is the main body of the CNC machine tool, which includes the main moving parts of the machine tool, the feeding moving parts, the executive parts and the basic parts, such as the base, the column, the worktable, the saddle, the guide rail, etc. The main movement and feed movement of the CNC machine tool are driven by a separate servo motor, so its transmission chain is short and the structure is relatively simple. In order to ensure the high precision, high efficiency and high automation processing requirements of the CNC machine tool, the mechanical mechanism of the CNC machine tool should be It has high dynamic characteristics, dynamic stiffness, wear resistance and thermal deformation resistance. In order to ensure the full play of the functions of CNC machine tools, there are also some supporting components (such as cooling, chip removal, protection, lubrication, lighting, etc.) and auxiliary devices (such as force meter, programming machine, etc.)
For CNC machine tools such as machining centers, there are also tool magazines for storing tools, manipulators for tool exchange and other components. The machine body of the CNC machine tool used the ordinary machine tool structure at the beginning of its birth, but made some changes in the automatic speed change, automatic positioning of the tool rest or the worktable and the handle, etc. With the development of CNC technology. The technical performance requirements are higher, and great changes have taken place in the overall layout, appearance, transmission structure, tool system and operational performance. Because the CNC machine tool has a large amount of cutting and a large amount of heat in continuous processing, which will affect the accuracy of the workpiece, its processing is automatically controlled and cannot be compensated manually. Therefore, its design is more complete than that of general-purpose machine tools, and its manufacturing is better than that of general-purpose machine tools. Machine tools are more precise. |
